There are several plug and code or whatever you want to call them tools being made. For now I believe all the big three are working on these for their mobile OS', with varying degrees of success, but where heading to a future wherea lot of neat "simpler" apps canbe made entirely by designers with an idea and no coding.
I think the only apps will be (and currently are) simple enough to do that are simple RSS apps - apps that are auto-generated to provide content from a website or RSS feed. Give it the URL and color scheme, and you're good to go. There are a couple services that do this. Short of that, it's impossible.
And Instagram could replace Photoshop... if you're not a professional. Same with what he's suggesting about Visual Studio. Visual Studio is not a toy. It's serious business. You can drag and drop UI elements, but no matter what you're going to have to write the code behind by hand [even if some of it is boilerplate/standard stuff... actual application logic will need careful consideration].
^ All changes if we get some serious AI. But that would be a very scary world.