I know I'm not a regular here, but I do love my pogeymanz, and wanted to share a few thoughts if that's all right.
First, I don't think the first step of the EVO project should be a Concept Poll. As was mentioned, the idea of choosing to evolve a previously existing pokemon as opposed to just creating one from scratch is inherently "fanboyish". In regards to the metagame, it's irrelevant and arbitrary what a pokemon evolved from. If we wanted to begin with a Concept Poll, then we might as well just turn this into CAP.
(I think the above has already been established, but it's worth repeating.)
The purpose of the EVO project should be "fixing" previous pokemon and their respective gameplay mechanics by giving them a means to become viable in the metagame while retaining their identity and unique gameplay niche. This ideology treads less in competitive territory and skews more towards effective gameplay (re)design and (re)balance. The OCD in me loves this type of stuff, seeing as how I can't stand to see gameplay mechanics being underutilised or improperly balanced (in any game).
So, that obviously means the pokemon that we are to evolve should be selected first. By whatever means you all decide on.
However (and this is the real point of the post), I really think there should be a Concept Poll AFTER the the pokemon is selected. I can't stress how important I think this would be. Without a specific direction, all the EVO project might do is, say, buff a Lumineon evolution to Borderline because, despite adequate stats and movepool, fails to do anything others in OU can't do better.
Or something. The specific pokemon doesn't matter. The point is that a Concept or Role will ensure that a pokemon doesn't become redundant in its gameplay niche, and allows others to stand out from the pack better. Furthermore, some pokemon don't HAVE a definitive direction (like the previously mentioned Spinda), and a Concept will anchor the project towards a specific goal that will benefit both the pokemon and the metagame.
When considering an evolution, there should be three parts:
1) Consideration for the pokemon's previous role and gameplay mechanics.
2) Consideration for what parts of the pokemon's role could be expanded that would allow it to maintain a unique position within the metagame.
3) A bit of fan creativity (while still remaining competitively viable).
It would be a shame to see something like a Spinda evolution result in just a generic all-around stat buff with movepool expansion. Rather, it would be interesting to, say, expand on the idea of the confusion status and incorporate it into the already topsy-turvy Spinda, using gameplay mechanics ranging from buffs/nerfs based on confusion status, moves that have their efficacy (damage, accuracy, crit, etc.) depending on who is confused, or just a general expansion on what the confusion status entails. All in addition to the usual stat and movepool buff, of course.
Or, take Luvdisc, and do the same thing with the attraction status. It would be better than turning it into Starmie's twin or something.
(Also, take note that part 2 would certainly allow or even invite new type combos, while part 1 would suggest that at least one older type remain. Also: Moves and Abilities.)
Basically, I'm saying that new gameplay mechanics that further expand what the game of pokemon is capable of depth-wise would not be possible without a Concept vote. Without it, we may find ourselves struggling more than once to differentiate a great many pokemon that are all too similar, with only the best of them being promoted to the OU tier (and leaving the rest of our efforts in vain).
Bah, I'm done.