It would make a really fun scenario where post-ending you'd be able to play as a feral Donk, scouring the facility for anymore survivors to transform, but with the scope of the game in its current form, it'd just be waaay too much to implement sadly. Though do note that you can be both 10 Infection and 10 Donkey-Brain and still progress through the game, battling your Donk-thoughts and desires in vein attempt at remaining Human mentally, whereas your body is already turned past the point of return.
However, maybe in the next game (or DLC) it'll be more Donk-focused ;3