Given the iPad is a closed and proprietary platform, I doubt that porting Emacs to run on it is very high on the roadmap. Probably a greater chance to see it on an Android tablet (and I'm not sure how 'open' Android is either!).
I suspect there would be significant challenges to getting Emacs to work on a touch screen device. In the meantime, best bet is to run remotely over ssh. Personally, I find coding on a tablet to be a pain - rather use a notebook running GNU Linux - light, small and full access to all the GNU utilities/tools which enhance Emacs functionality, plus all on a familiar filesystem.