New idea: MewThree plus Silph Co.
Mewtwo had the power of all pokemon, and MISSINGNO could become any pokemon.
Porygon was the virtual reality pokemon, and MISSINGNO was a glitch, glitches can occur in virtual realities.
And when the Silph Co. Lab was gone (G/S) so was MISSINGNO.
I think Missingno should be reintroduced as MewThree. Being a glitch himself, the pokedex in unable to identify him, dubbing him Missingno, the number missing from the pokedex. He should team up with MewTwo (his "brother") and do some stuff. Team Rocket tries to control him, and you join them, because Team Rocket control him would be better than letting his destructive powers run free. Silph Co. would have a new base and finally be the center of the plot, as the creators of the Pok'eball should be!
Wasn't that your idea of a hack game? Or somebody else's.
Fighting/Dark/Psychic isn't a proper trio, as Psychic doesn't effect Dark.
Things like Rock, Flying, Fighting would have worked, but since they won't create a pure Flying type, it wouldn't work.
Basically I'm trying to say I hope they stick with Grass, Fire, and Water. :) But the final evos could have Rock, Flying, and Fighting in them, or other three types that work the same.