Im sure if anyone with decent art talents (maybe look in art forum?) could finish these if anyone really had the motivation to do so. I dont think Devan is necessary really. At some point adding all these new things will begin degrading the games quality until its like that mushy stuff you find in the fridge.
If you really wanted it wouldn't surprise me if someone in the community (Specifically tileset designers) would be able to pull it off. But then really, how many ppl will care. and plus fighting Devan's final boss as Devan would create a time space paradox and destroy the game anyway.

IF Jazz 1.25 really needed new features, id say a better HUD/GUI, increased amount of bits so you can have more warps/trigs, and some upgrades to JCS, of course the minor bug fixes here and there, and Epic if they did it would prob add a few new enemy's and tile sets in.

I personally, have always wanted an option under JCS for the enemy's to be able to set a health, so some weren't so easy.

The more greedy you guys get about adding big things, the less likely that they actually be implemented in the chance that further development does occur