I've got an idea. How about instead of having the Dual Identity class feature, there is an optional ruleset where PCs (and NPCs) can have a Character Background. It would provide minor crunch and features for a variety of different backgrounds, with additional features granted at 1st, 2nd, 6th, 10th, 14th, and 18th levels (levels where PCs don't get any non-class abilities like feats and ability score increases).
Dual Identity could be one. Others might be Folk Hero, Noble, Pilgrim, Hermit, Urchin, Pirate, Sailor, Merchant, Master Craftsman, Tinker, Priest, Savage, Feral Child, Academic, Constable, Seeker (journalist/scientist/detective), Courtesan, Courtier, Jester, Apothecary, Hedge Witch, Witch Hunter, Criminal, Charlatan, Outlander, etc. etc.
EDIT:
The power level would be something around Trait-level. It would mostly be flavor, but would really flesh out character concepts by giving a little crunch to what is usually mostly fluff.
Except there is no way you could have one for every profession. Which limits concepts in any game it would be used.
You could make it modular and customizable and general. A lot of this is inspired by both 5th Edition Backgrounds and PF Archetypes.
Ehh... I really hope the dev's stay away from 5e's background things. Hated them in 5e, would hate them more in PF.
I really like them. I think they're a fun design space and can help make both more versatile and more focused characters.
But to each their own. :-)