Hi David,
I am thinking too.... thinking .... thinking but have not really start yet. I have chosen to start from the classroom rather than from Joomdle - only because my need is there at the moment.
As for Joomdle, there has been no work on that at all.
There are some template providers that will help, for example yootheme has responsive templates which will partially help. I see one of the biggest problems, regardless of template providers, is that much Moodle content may need to be redesigned for different screen sizes. Videos, should be able to be handled by the responsive templates (but remember moodle video tools will need to be responsive too).
Have you looked at how the Moodle apps work for iphone / ipad. I did a quick search a few weeks back and notice a few apps but didn't really play with many. The first few, were not fantastic but perhaps I didn't give them a good kick.