I think a good app would be called “TROOPS”, where you tap your phone whenever someone was in the army and it goes “Thank You For Your Service™”. People who say stuff like that a lot are a market ripe for disruption.
It’s easy to monetize because the target customer likes novelty, so you can sell a lot of new voices. And what underemployed 20-something wouldn’t appreciate a good patronizing from Batman?
And then you have a $4.99/mo Liberty’s Hammer membership where it adds “…and God Bless America™” whenever the app talks.