I hope to not sidetrack a focused discussion of ENSIP-14 in this thread. But wanted to add my agreement that adding an option to register in a single transaction without any need to commit is a great one !
We can keep the option to commit + register for the people who want that. The mass of the market would prefer to reduce all the overhead and complexity from that. The platforms that are processing these registration requests can just make use of flashbots or other relays as you suggested.