yeah so the answer to your first question would be a "no" then. in banning Evasion and OHKO moves we acknowledged from the beginning that "something is wrong with the game that we are currently playing," "Double Team and OHKOs are broken moves, or otherwise prevent us from reasonably deciding who is the better player of this game." Whether or not that is what "we" literally decided as our reasoning (who knows, people back then might have thought "Double Team is just toooo annoying let's ban it!") is in my mind irrelevant, for the very fact that said reasoning did exist so we could justify a "test" (I'm assuming it was in reality just an outright ban)
you are wrong about why "we" banned DT and OHKOes back then. i have tried to subtly hint that i was playing competitively in 2000 and therefore know what i am talking about, but the subtlety seems to be lost on you so i will be blunt: i was playing competitively in 2000 and therefore know what i am talking about. dt and ohkos were banned because they were broken, not because they were annoying.
and the key word there is "were"—today, dt and ohkos are under consideration not because they are possibly less annoying, but because they may not be broken in platinum's metagame.
So no, based on what you've said so far, there is no precedent for us banning moves purely in the interests of a better competitive metagame. Just for moves that we can firmly establish are either broken, or otherwise pose as a clear obstacle between relative skill and relative ability to win (which I would call different from "broken" most of the time but either way DT and OHKOs at least at one point did fit this description)
the difference between the two is semantic as best, and anything that we have, had, and will have considered will be so considered in the "interests of a better competitive metagame" and nothing else
which part are you talking about? I'm hoping it isn't the one that apparently contradicts like the entire reason behind a Stealth Rock test.
"Smogon attempts to avoid bans as much as possible - only when it becomes very apparent that a Pokemon is far too powerful to be in line with a balanced metagame is it banished permanently from the standard arena."
If you're wondering, yes, this is exactly one of the reasons I asked the initial question of "where the line is." If we're now suddenly removing that little bit of the philosophy and replacing it with "we'll test anything we might be better off without by relative PR consensus" then I want to know why we're supposedly willing to go that far, and not directly into the realm of directly altering game mechanics.
If our goal has become to determine the "best possible OU metagame," then yes, I think a slippery slope is not out of the question at all. Trick has already had its smattering of complaints, after how many weeks of Platinum play? At the very absolute least we are promoting unhealthy "CalmCune is 00ber" type behavior and discussion amongst less experienced/informed players who now think that anything they hate playing against deserves to be tested. In a community where a number of people over a range of skill levels can be convinced that Magmortar is an amazing mixed sweeper, I'm definitely concerned with what could happen over the course of the year, or especially a generation if it comes to that. No I'm not worried about things like Double-Edge, but I fail to see how this isn't at least a somewhat legitimate concern.
its not a legitimate concern because it is not a coincidence that i both created and am heading up the suspect test process—i have been involved with competitive pokemon for over eight years now and have learned, among many other things, not to jump the gun on assessing new pokemon.
you reference "CalmCune is 00ber" (or "Calm Mind Suicune has no weak", depending on who you are), a sentiment which never got any actual wings when it was used in play because people realized it indeed was beatable, contrary to the preemptive theorymon spread by those who value theory over practice.
you reference Trick but yet either forget or are ignorant of the fact that I personally and purposely decided that we should test Deoxys-S before Skymin so people could actually gain some experience with it before crying "uber!", as they largely were in its first week on the standard ladder, much like they are doing with Trick today.
you reference magmortar...are you serious? skiddle himself will be the first to admit that his thread was an utter failure in actually revealing magmortar to be
a mixed sweeper and not in actuality a wall breaker. the people that were or are "convinced that Magmortar is an amazing mixed sweeper" are the exact same people who are not going to have any say in the adminstration of these processes until they learn what competitive pokemon is actually all about, like i have, which is the reason you shouldn't be worried.
and finally, you're attempting to tie these three points (calmcune, trick and magmortar) back to the Stealth Rock issue, which does not apply because those three were or are all preemtively judged in mere weeks (or days regarding magmortar) as being stronger than they really are in practice, whereas SR has been used in practice in the metagame for almost 1½ years now and we are therefore going on a wealth of information
Edit: Also, the decision to test Stealth Rock itself could potentially influence votes on other Suspects. This might have more to do with the voting system being questionable at best than anything though.
this is why the suspect test process has three stages, and, further, why we would consider testing SR now, in a metagame with as few stage one or two suspects as possible after skymin is decided on, so we would be testing it as the lone suspect (if skymin is voted ou it is therefore no longer a suspect until stage three), as we do with all the suspects