If the current client works, then what is Dropbox's obligation to provide a new one? As I understood it when signing up for a 50 GB account, my payment was for increased storage. There is no sales language on their website indicating that I'd benefit from any future features. They don't sell you on future benefits, and looking at their features page [1], I don't see any language that would imply anything to this effect either.

1 - https://www.dropbox.com/features