From what I remember, those old tech mods that added coal coke had it power minecart trains just as coal and charcoal do. This is not the case with cotton resources's coal coke. While clicking on a minecart with it does cause it to move, this happens with pretty much every other item and the lack of smoke particles emanating from the furnace shows it's not actually powered.

yeah, I'm surprised that it doesn't ask abstract furnace whether the item is fuel

It's hard-coded for coal and charcoal, with a fixed fuel value. Changing that is out of scope for this mod in my opinion.

B0oundary has an idea, but that won't be in this mod.

Huh, I'd expect the minecart furnace to use the fuel tick registry. I'm pretty sure Falk expected that too, so we didn't think to mix into the furnace cart to make it support other stuff.

seems this ought to be closed.
also in case someone stumbles on this, i added this to the item compatibility mod i made:
https://github.com/Linguardium/ItemCompat

Item Compat should definitely help with this. Since we don't really wanna do those mixins ourselves, I'm gonna close this for now.