I suggest a Kingdom Run based RPG flash game or ipod/pad app. You choose an original class (soldier, archer, or mage) and as you level up gain new pieces of armor and weapons (and later upgrade your character to different types and eventually make a final specialization). This may still be some kind of RTS or at least strategy of some kind, but with an element of RPG mixed in. Honestly you could make a great MMO off of this but I know that would be too much trouble (I would definitely play it if you made one though). Anyway, I don't pretend to have perfect ideas but some kind of RPG based on Kingdom Rush would be great to see.
EDIT: I called Kingdom Rush 'Kingdom Run' by accident.