I know this is a long shot and probably won't ever happen. But, thought I'd start a topic to see what the community thought about this. I wouldn't expect every feature to be packed in a theoretical iPad/iPhone version, just the basics like importing parts and doing basic animations. Then, sync it back to the desktop application with iCloud or Dropbox or whatever for the more advanced stuff.
I think this would benefit users on the go. Somedays, I'd bring my iPad along with me to the park and doodle a little when resting at a bench, for example. And I'd be able to do this instead.
As far as I'm aware, there isn't anything like Spriter on iOS (If there is, please let me know!), and I'd personally love it.