I just thought I'd add that you probably haven't done your research very well. Yes there are a lot of crappy games on iOS but that isn't to say that RPG fans aren't well catered for on the platform.
If you are aiming your game at genuine RPG fans then you would be up a giants Baldours Gate 1 + 2, Iceland Dale, Legend of Grimrock, The Bards Tale, Several Final Fantasy games, The Avalon games from Spiderwick software, Coldfire Keep, Banner Saga and tons of others.
A very important point!
Not only are there actually pretty decent original RPGs being made for the mobile App Stores (not all games released for mobile are shovelware), but a LOT of re-releases are finding their way to the mobile App stores as of lately.
And no matter what you think of the original graphics of the time, or the 8bit retro style, these games often get refreshed graphics, and in some cases these are actually pretty good!
I own pretty much all the old Final Fantasys (up to FF8 where Square lost me as a customer) on the original consoles, but if I had a good device with iOS or Android that would allow me to use a controller and hook it up to the TV I would probably splash out the 10-20 bucks to play a suped up version of FF6 (I know my mobile phone probably could do that if I would splash out for a bluetooth controller and would do some additional work, but this is already a little bit too much work... ESPECIALLY when I am not sure that the dev didn't gimp the RPG by making it controllable only with touch controls ).
Now, not only are these games actually looking pretty good even by modern 2D mobile game standarts thanks to the graphical rehaul, and have a pretty big fanbase (which happens to be older, thus is the fanbase that actually has money to spare), they have also quite good storys.
Trying to outdo the Story of FF6 will be a tough call for example. I guess the same could be said about Baldurs Gate.
Will certainly take more than 3 seconds.
Is the average quality of RPG storys on mobile way lower than that? Of course. But when only the top 10-30 RPGs get any meaningful downloads, you can discard the others as benchmarks. You will have to compete with the big ones, not the shovelware that nobody looks at.