The HTML Media Capture interface is starting to be supported; Android 3.0+ tablets and upcoming 4.0+ handsets support it directly
Even before we worry about mobile-specific interfaces, it might be nice to accept photo (and at least in theory) video uploads through Special:Upload etc over this interface when it's available.
In principle, this should work as additions to <input type="file">; if the 'accept' attribute has various types set, it should be able to prompt for capture modes as well as local files. Need to check whether this already "just works" on eg Android Honeycomb tablets or if we need to add the settings to get it to trigger.
Can also use the 'capture' attribute to indicate a preference for capture. Not sure if any special UI would be appropriate on general interface.