I would easily pay 15-20 dollars (I live in Argentina, where that’s quite a bit of money) if it did what I expect from it and it’s properly supported - maybe a bit more. (I’m trying to be within reason of what iOS app cost - that I know it’s sometimes too little, making it hard for developers)
I’ve done some beta-testing (Shoom and a few others) and I’ve been craving for something like this (either hardware or software) for a long time, and I’ve posted here and other places many, many times, at the point of sounding like a crazy person.
So if you ever decide to give it a shot… let me know 
I’ve harvested ideas for this for a long time (probably not alone here) and I like to think of myself as a somewhat-reasonable person (meaning I’m not going to ask for the app to make pancakes as well)… also a graphic designer and a nerd - what I mean to say is: my heart is in the right place hehe