If were going to go this far, and especially with giving new evolutions and prevolutions, I say we mix things up a bit. Obviously we don't need every pokemon to be viable, especially NFE ones, but Copii with all 24 is about as useful as a burned caterpie lol. By adding these pokemon we can adjust already designed pokemon to make them fit in the evolutionary lines better.
Since Ditto is relatively weak as it is, since he's gaining a prevolution, I would suggest bumping Ditto up just a tad to make it a more appropriate stage 1 pokemon. I would think something like straight 40s would be more appropriate for Copii, or even straight 35s.
We can also design how to implement these pokemon into the game. Like perhaps you can't find Copii in the wild but you can get one from breeding 2 ditto together (where as ditto + anything else still becomes anything else).
I also think mixing together some other Pokemon like Arbok evolving into Seviper should be considered. I really don't understand why that isn't the case as it is, especially seeing how the anime made that mistake as well lol
I think Cromix is my favorite so far. That is sooo cool.
Also if we do fusion evolution Dodrio + Exeggutor could be like Exeggork