Many competitive players despise the notion of a metagame with "significantly more variety" than 4th gen OU already had. Most others probably don't care one way or the other. There is some minority that actively craves a metagame with a greater number of viable teams, and out of those, maybe four or five are out there preaching that "removing" Species Clause is the way that this should be done.
I am very much operating under the assumption that we should not implement Species Clause unless there is a reason to implement Species Clause. We know, however, that the only benefit you're suggesting (besides a simpler ruleset) basically has no "market" for it in this community. Even if we polled Uncharted Territory and they decided that Species Clause should not be implemented in the beginning of 5th gen, my impression would be that they just thought it was potentially superfluous, or that it could be "interesting/fun to mess around with," and not because of some belief that the increase in variety brought about by its non-implementation is competitively preferable. In other words, I can only foresee the community supporting a no-Species Clause initial metagame under false pretenses--once players realize that the clause is not superfluous, and indeed restricts a number of otherwise-viable team strategies (something that I feel they are largely in favor of), it will be re-implemented.
I guess I could be wrong, and really everyone is clamoring for much much more variety without me knowing it. Okay, then it becomes a question of whether the increased variety (which can now safely be considered a "benefit") outweighs the potential issues I spoke of earlier. We aren't at that point yet at all, though, because the "benefit" you're suggesting is a controversial one at best.
I'm tired, so sorry if this doesn't address your points precisely, or if it restates things I already made clear or whatever. could easily be both >_>
