Core Data + NSIncremental store with a web api backend does not solve the problem of offline sync. It is possible to roll your own, its hard to get it right. It is complicated by iOS restriction of not able to run your own daemon. But then if I have the resource to roll my own then I would not complain about Apple.

Dropbox does not come close as alternative. Dropbox as of now is file-based sync. Core Data iCloud sync is trying to sync an always opened SQLite3 database file, they do it through database log files. Possible alternatives are TouchDB, Simperium, Firebase but then you have to change your app from not using Core Data. Or rewrite your app to use file based storage as what 1password did. The key is offline sync. File based cloud sync is solved problem. So maybe the way to go is persistent store of client app has to use files.