<< as there would be a pinnacle evolutionary point at which no environmental alteration would even remotely affect the species, regardless of what it is. >> Thats not really true. If you drop a species in to a new environment then of course it will change.
Again, there is a pinnacle point at which a species will have experienced and adapted to every possible environment they will ever encounter.
<< It's actually been shown to happen in simple organisms >> Yeah ok, but its like saying mutations can happen and then making the leap to the Teenage Mutant Ninja Turtles. Possible but not probable.
Actually my example is both possible _AND_ probable. This happens in roughly 98% of amoebiotic life forms subjected to such tests. The part that makes it so spectacular was that it was done in an entire species., showing just how advanced the precursors were.
<< Not introducing any new elements? >> Yes, just base the game around a war or new colonizing efforts or something like that. I realize that they did what they did so they wouldnt have to use copy written material though.
A war or a new colonizing effort would be a new element unless it was still focused on the Doctrinal Conflict. Not introducing new elements = copy, not sequal.
You listed a whole bunch of proof of concept items and I will conceded that if you are willing to stretch far enough you can make just about anything sound possible.
You mean like alien races having an all-out throwdown in the future and humans actually being advanced enough to participate alongside aliens millions of years older? It's a video game. Lighten up. I just wanted to point out that the things you said are impossible aren't.
It still is not plausible though. You can almost believe some stories but can you almost believe Ninja Turtles, Digimon, Spider Man, or SC3?
I believe any of those things as much as I believe SC1 and 2. I've accepted that they're only fantasy, and while sometimes based a bit more or less on science, they're no more real for it. So, all in all, SC3 and your favorite example of "Ninja Turtles" are in the exact same reality category as SC2 -- Not One Bit.