Something I've noticed is that fire doesn't provide heat. Could this be added as functionality, and possibly disabled with a config? Perhaps it could even be setup to be a list of blocks defined in the config that provide heat or cooling.

Yes. I've noticed that also. Fire means nothing. Get Netherrack block and ignite it and it does nothing.

The issue with fire. Is that block temperature will over ride material temperature. I don't think if you are standing on a block that might have a temperature that is lower then fire. It should over ride fire.

I believe this was resolved awhile back in newer versions (1.12 definitely, 1.11 too possibly?)