Comment 4 for bug 843256

X does have a panning functionality. It's unfortunately buggy when used with unity so not something that could be easily switched on, but certainly possible. Most of the work would be the window management work to enable it when appropriate.

I think this is mainly going to be a UX/Design area to decide, so am reassigning to unity.

Meantime, you may want to file bugs against particularly problematic applications, to get dialogs that fit within the screen realestate. Even with panning or scrolling, it'd obviously be preferable to be able see the full window in the screen.