I would argue that such a thing already exists. If you want to do 'easy', low-hanging, easily-prototyped design and development, the kind of experience you had as a kid with Hypercard, you can still do it, and mostly for free: it's the web.
A hypercard-inspired tool for creating touch applications is going to be disruptive, and is going to happen. It's a glaring gap left open by Apple. In fact, this is the reason I am personally hesitant to start working on one, it's so glaring that I would be surprised if Apple hasn't been working on one that will be released when it's ready.
I couldn't agree more, and it's why I'm so enthusiastic about the web as the lingua fraca of computing. But as Steve might say: "Not good enough yet; make it again." To put it mildly, I think we can do way, way better.