Thanks for the question, but unfortunately, no. Since the scrapped Floor Builder uses a different JSON data structure for it's custom floors (stored in a .floorlvl data file) compared to the under development Floor Maker for the upcoming Beta 1 update (which is planned to use .bfnsu data files for it's floors), porting custom floors made with this prototype is not possible.
Although for the community made schoolhouses in Ultimate's Random Floor Fun (formerly called just Random) mode, I could perhaps try to recreate some of the floors created in this prototype (such as ones by you or other floor makers), so some floors made in this prototype would still have a chance of appearing in the main BFNS Ultimate game.
I'm looking forward to seeing your creations in this prototype, as it still lets you get really creative with custom floors, and maybe like I've done in the past, I'll do a video (or several) where I play custom floors created by the community.