Moving right along....
Nomark's Sacrifice: I don't see this working at all. Being KOd is bad. Unless we add some absurd custom mechanic, which we won't, it is not possible to be of more value dead than alive. You'll need a lot more justification for something like this.
Korski's Weather Warrior: Well, as you say yourself, it is very similar to jc104's concept, but there are key differences, specifically in how yours is supposed to help exactly one weather, hurt exactly one, and only be able to do one role at once. I think this would at the same time give more options and make the project more focused. I can't say for sure which of these two weather concepts I prefer, but this is a very well thought out concept, and I can't really think of anything that needs to be adjusted.
capefeather's Faustian Bargain: Huh. Definitely an interesting one here, but I'm not entirely sure what to make of it. This takes that common "Let's do one thing awesomely but suck everywhere else" concept and actually makes something rather interesting out of it, which is pretty cool. However, I'm not sure I really see one Pokemon being able to do both roles well, at least not a Pokemon that comes about via the CAP process. This would mean the "base it on an existing Pokemon" rout would be the most likely way to go about things. I think its a cool idea, but it gives me vibes of being both too vague and too complex at the same time. It definitely has potential, but I'm just not really sure what to think at this point.
zyrefredric's Small But Terrible: Now, I'll be honest here, I would love to see a low BST Pokemon for this project. However, I just cant really see that in and of itself being a good concept. One thing we have established here is that when it comes to measuring a Pokemon's strength, BST means little to nothing. However, that does not mean that doing something with a low BST is better or more informative. In fact, low BST alone can't really teach us anything. Really, there is just not that much that we could get out of this concept in the end, in addition to the fact that the concept as is is way too vague.
Solstice's Leading the Charge: Leads are an interesting facet of the game that do not really exist anymore, so exploring how to make one shine again has some merit. However, I'm worried about how viable this actually is. I don't see anything glaringly wrong with it, but I would like to see a bit more as far as what some learning goals would be cause I would want to be sure we would be getting something out of this if we attempt to go this route.
DarkSlay's Utility Counter: Take Two: Well, it's a solid concept to say the least. My biggest personal problem is that I simply don't find it all that interesting. I feel like versatility, but not all at once, is something that we already know a decent amount about, and while this could key us in to specific things about the current metagame that may not be currently known, it won't tell us anything new about competitive Pokemon as a whole. There is absolutely nothing wrong with this, but I'm just not really sure this would be the best way to go.
QuimicVital's Legacy: The concept of making the Pokemon that follow dangerous rather than being dangerous yourself is interesting, but the concept as is is way too vague. I would have no idea where to even start. And the fact that you say you can't think how to not make it OP doesn't help. This definitely needs a lot more detail as to the goals of the concept.
ReddyGo's The Core Issues: I always considered concepts revolving around specific interactions with existing Pokemon in an attempt to learn about general cases of Pokemon groups (in this case cores) interesting, and this is no exception. That being said, I think the way the concept is currently written leaves it a bit too open ended. I'd like to see more of what you want to accomplish by making it part of a core. Simply making it is cool, but what is it that we want to get out of that?
Delta Nite's (via Birkal) Perfect Nemesis: Liked it then, like it now. As the previous concept, this gets into a specific case that can teach us more about how Pokemon as a whole interact. I feel it can teach us a lot, and is also very focused while still giving us many options as to how to go about it.
Eagle4's Two Sides of the Same Coin: Well, I have talked about vagueness on plenty of concepts already, and its the same thing here. You say you want a Pokemon that can do the same thing but in multiple ways, but you don't even hint much at what that means. I personally can't see how this is going to work, since if you can do one thing two ways, one will in all likelihood be superior. You rarely see Pokemon with multiple sets for any one role. If they have multiple sets they are for doing different things since you can only do one thing so well. Of course, maybe I am misunderstanding. Vagueness is definitely the biggest problem, so I can't comment on much else unless you add more detail.
Pwnemon's Hazard Control: This is definitely the most interesting take on a hazards concept I can remember seeing. Setting and spinning are talked about every single project, and bouncing them back relies on their existence to begin with, so trying to solve the "problem" by simply going down that route would be boring. However, actually trying to tackle the problem of hazards not by essentially changing the hazard culture itself via threatening the setters and discouraging people from wasting the team and time on it could be a fascinating project. I am concerned however that little of what we would learn from this would be applicable to an existing metagame. In that vein, I would suggest altering the questions section (which also looks like you may have forgotten to edit when you altered some things), to focus more on what this could teach us about hazards or the meta itself that would be applicable to OU.
SubwayJ's Plain Jane: Hmmm.... well... I'm not exactly sure what to think of this one. Its odd, but not to the extent that I would call it a bad idea. However, I don't really see us learning much from this. Maybe you can provide examples of what you are hoping to learn, but right now, I don't really see the point of it.
inanimate blob's Martyr: As with the above concept, I can't really see what we would be getting out of doing this concept. What is it supposed to show us? My other concern here is that such a Pokemon would need to be extremely good otherwise why use it over something else that can work well without hurting itself? I think these are questions that need answering before we would want to consider something like this.
nyttyn's Last Stand: So I've said this many times already, but I'll say it again, what is it that you want to get out of this concept? What is there to learn? I think this concept has a lot more potential than some of the others that seem to lack goals, but, as is, there is nothing in there that suggest why we should do it other than that it would be cool and interesting to have a Pokemon that fits into that role.
pokemon0078's Holder of the Dice: While I have a feeling any hax related concept will be controversial, I do like things revolving around luck management. I think this is something that we could learn things from, I am worried that it may have problems similar to our most recent concept. I think the best way for this to be clarified would be to give more of a concept for the Pokemon itself. Right now the concept has potential for a project, but is too vague for a specific Pokemon. I'd like to see the specifics of this developed a bit more.
And so ends page two. Going to go have some dinner and then will continue responding to the rest. Before I do that though, there is one thing I want to address. As I said at the beginning of this thread, the questions section is probably the part of a concept I scrutinize the most, and as you may have noticed, there have been many concepts about which I have mentioned that the questions could use improving. I want to take a moment to let you all know what kinds of stuff I am looking for.
Here are some examples from this thread of questions that I think are great:
"What defines a "core"? Celetran, Toed/Ferro/Jirachi, etc are all considered "cores", but we do not have a standard "definition" for one. Is it just a triplet of Pokemon that work together very well in unison, or a pair that has perfect coverage on the meta?"
"How does negative momentum affect the flow of battle?"
"Is a types usefulness relative to the metagame or is it intrinsic? (Ie. Can any type be the "best" type given the right circumstances or do type match-ups, available STAB moves etc mean some types will always be better than others?)"
"Bearing in mind that weatherless conditions offer minimal advantage to any team rather than sand or hail, is it even possible to restore weatherless teams to their former glory without banning stuff? Or is it mandatory to pack a Tyranitar, Hippowdon, or Abomasnow just to keep the other teams in check? Is sand the new weatherless?"
"How does weather control play into teambuilding? Is preparation required to confidently neuter an opposing weather team, or is superior gameplay enough?"
"What exactly is a counter? What is a check? How does the good-but-not-great Pokemon use these definitions to take on the Perfect Nemesis?"
These are detailed questions that get into things that we want to be learning as we go through the process. On the other hand, there have been plenty of questions that I would prefer you stay away from. Its not that these are bad, but that they are obvious. Simple things, often about collecting facts after the process is over, and not about being focuses for discussion in the process itself. They are not something we are out to learn, but things that are an innevitability of choosing the concept. Usually these are things like "Is it possible..." or "How will X effect Y." Here are some examples of what I am not looking for (note: I am not trying to pick on anyone. I am just using these as examples. If one of your questions appears here, than just take it as a suggestion to try and think of some more like the first group):
"Is it possible to have a pokemon be able to perform a multitude of roles, despite a small movepool, without relying on high BST, extremely powerful abilities or weather reliance?"
"How would the addition of moves such as "Tail Glow" or "Swords Dance" affect this priority abuser"
"What kind of strategies could such a Pokémon pull off?"
"Did this Pokémon make Stall more used, or did it do the exact oposite?"
"Will there be any Pokemon moved into OU with the introduction of this Pokemon?"
"Can a Pokémon that harms, but not sacrifices, itself for the good of the team be competitively viable?"
"How good does that pokemon have to be?"
Anyways, I hope this helps, and I'll be commenting more on the rest hopefully later tonight.