Man I'm getting déjà vu, I remember this discussion happening back in 2015...
I think restoring the custom title option to Patrons would be a good move. Though the simplified scheme of the Patreon may make that hard to manage, since it would apply to all Patrons.
One way of resolving that would be to have it apply to only people that are both Masters and Patrons. While that may seem a bit too exclusionary, I think custom titles warrant a steep investment.
In this suggestion if a person loses Master or stops being a Patron, then they'd still retain their title, however they wouldn't be able to have it changed unless they regain the status of both Master and Patron.