I would go about making Ubuntu into a development environment through the web. There are various points in the browsing experience when a visual HTML editor could be useful, then in the visual HTML editor, touching an element could drop you down into JavaScript to add events. In the same manner, more complex constructs could be progressively introduced to the user.

Furthermore, I personally use versions of Android on my tablets and Ubuntu on my desktops. I see no reason that Ubuntu should "make a dent in the tablet market" when Android is already doing fine for us.