Earlier quoted context omitted.
I think the biggest problem comes from supporting external displays. For me to fully swap to iOS as a development platform (ignoring missing software currently) I would need to be able to plug into a larger display at some point, and have a way of controlling apps on that display without using touch at all.
Once you get to that point, though, it seems like what you're really looking for is a computer and not a mobile device. Perhaps what's missing is not an iPad with mouse support, but a Mac with a more Surface-like form factor.
Android does support mouse input; Apple can at any time release a typecover for iPad with a trackpad. They choose not to.