I don't know any but that seems a very good idea. But if you haven't tried Doodle Sky HD perhaps you should. It's not a RPG but there"s a global story and missions are very diversified. There's no class but you can unlock some planes with different characteristics to choose among those you unlock for doing a mission. Some people can't get used to its controls because it's not a pure free line drawing control. You control only one plane and to make the play more interesting and simulating dodge fighting and that drive a plane isn't that easy, your line drawing is constrained by limits, you can't draw a line that turns too hard. Myself I get used to the controls very fast but clearly not everybody succeed. I think it's more advised for the ipad than the iphone because see the full map and have more space makes much more easy to learn the special controls. I have also another game to quote, it doesn't match line drawing RPG but there's some links. It's Knights of the Phantom Castle, you control 1 to 4 knights, more often 3, and you use swipe to move them and make them target an enemy, tap to trigger a special power depending of the class, long tap for another special power and a sort of quick light swipe to trigger a third special power. It's more a game like Syndicate with touch controls and an RPG Fantasy mood and background. Yeah it's not exactly a line drawing RPG and possibly have make moves like line drawing commands could have been a real improvement, or not if 4 lines at same time would be too confusing. Great game but difficult, as far I know nobody worldwide ever beat the second boss roughly at mid level, not really a challenge but more a game design problem. I already send a bug report complain to dev but still wait an answer, and as it's not indie I'll probably wait forever alas. Still for me one of the game the impress me an fascinate me the most on iPad. Again, I think the iPad version is more advised.
Yeah, why isn't there a Doodle Dungeons? The title even rolls of the tongue nicely! Matter of fact, I'd love something like Sketch Nation (the make your own doodle shooters) only for heavy duty dungeon crawling.