Epoxy over cementboard
Cement board isn't intended as a finished floor. It's not as dense as concrete. You'd find high heels and chair legs punching into it in short order, leaving you with a crumbly mess. Obviously you'd also have to tape all the seams and skim the screw holes, but you'd still have air voids across the entire surface to deal with.

I'd try epoxy over good (hardwood veneer?) plywood before cement board.