EPIC NEWS!!!!!!!!!!!!!!!!!!
Ok, I just talked to DanF (literally 10 seconds ago)
and he said that he WOULD start making the chars you suggested!
BUT!
-Knuckles wont climb walls (tho he will glide)
-Amy will be made without any downsides (well none that I know of)
-Eggman probably wont be playable (he didn't say that, I just think it's kinda pointless)
Oh! and if you've made any levels in the engine and send them to him, he'd LOVE to play them (yes, he said that) and he might add them to 3.0! (well he didn't say that but if he doesn't do it, I will

)