@wordjoy - I appreciate that you want something other than Dropbox. Candidly, if L&L could wave a magic wand and make that happen, I’d probably like that, too. But since L&L can’t do that, I do have to agree wholeheartedly with @RuffPub’s comments above. I’ve been using Scrivener on my iPad (and iPhone) for years using Dropbox sync the entire time. It has worked flawlessly (or darn near flawlessly) all this time. (I think a few years ago there was some kind of memory bug in iOS that messed things up for a while, but it was an iOS issue.)
There are so many things I’d rather see L&L focus on to evolve the iPad version than adding more sync-service options. This is probably a trivial thing for some apps, as @AmberV mentioned, because they are single-document model apps. Our Scrivener projects only look that way to us (on Macs, anyway), in reality they are a complex package of files. I can only imagine how much that complicates developing syncing solutions.