Some things i noticed is that the currently revealed Master classes are kinda limited in two major ways.
First that most master units are Mounted, with only 3 being Infantry.
That could mean lategame it will be kinda manatory to get all mounted, since otherwise 2-3 of your units will just be left behind due to lower range.
Second is that for all the Sword Fire Emblem jokes people like to make, only 2 master classes have a specialisation in Swords, with one of them being Female only(the Falconknight).
That means Male units that want to wield swords are currently stuck on being Mortal Savants.
Since there are 3 classes that have a Sword proficency in the tier bellow Master(Hero, Swordmaster and Paladin) it would really surprise me if they all had to become that, especially since that would mean their previous class requirements would go down the drain(the lance and riding for Paladin, and the Axe for Hero), since Mortal Savant does not need either of them.
Then there is the fact that the Lords and Byleth are essentially gurarnteed to have unique Master Classes, since anything else would be really surprising(my guess is a non mounted Master Heavy Armor for Edelguard, a Master Paladin Dimitry and a Bow Wielding Wyvern Knight for Claude.)
All in all it feels like they still have a bunch of Classes to reveal, since otherwise a multitude of class upgrade paths just look stunted or feel like they waste previous requirements.