We don't do sci-fi or stuff like that in our canon modern-time rp, so another human species wouldn't be plausible.
Like I suggested, if we have new landmasses, we can maybe have plots for historical rp, but in modern times there's no real connection anymore between the other continents and our main continent except maybe for imaginary trade.
As for your "Pacifica alliance" - I don't know, what you mean with that, but if it means that the South, East, West, North Pacific etc. should come together in rp....I don't think, it's possible? As far as what I have seen, rp varies bigly between the regions and so a collaboration between all the regions for the map doesn't seem to fit for me.
As for the climate:
Now that I think about it, you're right Qwert. I know of at least Seraph and Bruuma and you perhaps too using their given climate. But on the other hand I'm not sure, if I've seen Ryccia, Hammer or me caring too much about the climate. I guess, it's somewhat 50/50 between the current rp-ers, but I might be wrong too.
A REAL problem I'd see with supersizing TSP would maybe be the numbers. We currently know the area of our country, based on that we have population, based on that we got people/km², maps, military numbers etc that would all change. "It's just numbers" - Yes, it is, but those numbers maybe are much work in the end.

Anyway I think in the end a first survey on the forum on whether we should just supersize our continents or if we should add new ones would be highly appreciated.