It's very sad that Apple have neutered iOS so it can't even have apps decoupled from the storage of the files they operate on.

We'll be launching Dropbox support soon. Hope you'll come back to us then.

Something that may require some thought if you want to do this is how you handle import/export of documents with embedded scripts.

You'll need to be very careful not to fall to the "applications that download additional code" rule there. This happened to Codea (http://twolivesleft.com/Codea/Talk/discussion/comment/14504#...), and afaik they still haven't managed to get their project sharing feature re-approved.

Speaking of it: Support for WebDAV, SFTP, box.net, SkyDrive, SugarSync, AFP and SMB would be great too! (In this order.)

Otherwise a proper scripting language in a spreadsheet app on my iPad seems very promising. It would be also great if one could search public scripts of other users.