Would allow fully carpeted transitions from one room to another if desired. Not sure how possible this is, but it would be a nice addition.

I can't think of a clean way to implement this and still work with modded doors, I encourage you to just place wool under the block. Though might be able to implement a block is is just wool 1 extra pixel tall to serve the same purpose.

Thinking about it again, carpeted trapdoors kinda serve that purpose as their carpet is from the block below. Wonder if there is a way to make them support doors on top...