Different thought, to my original "they continue as they have been through the classes and then move on to [non-FR] setting-specific materials each UA" hypothesis...
Not overly likely to happen, but might be fun, if they took a break from just going through the classes and, still only having subclass options in the UAs, make each one a setting-specific...or do a set class (what's up next, Rogue?) with different subclass takes from a few different settings.
So, for example, the Rogue UA subclasses could be: 1) something broad usable in any setting, 2) Eberron Artificer, 3) Greyhawk Acrobat [based off Gord the Rogue].
Leave it to the individual tables if those setting specific types are usable in a given game or not. But it would make for a nice mix (and introductions) of setting material and different ways to view classes within a setting we may not have seen/thought of before -like considering Artificers as a type of Rogue, or as we've already seen, using sorcerer to get to a Favored Soul, etc...
They should do this.