I've been worrying about this. It'll affect a large number of pilots, and involve a lot of work for the FAA. Is any organisation willing to approach the FAA (or a Representative) to try to get them to accept the number changes?
(You cannot get a new FAA licence while the old one is valid, but it can be revalidated on a new licence.)
When my license number was changed from the old number system to the JAR one (due to an address change) the FAA Inspector spent a lot of time trying to find out why my old number had been revoked. He didn't believe me.