The sync/sharing/storage aspect of the product is mature given the relative one-dimensionality of file storage.
Storage, Syncing and sharing should be transparent to the users - so clearly, they need to ensure a continued robust, secure service - but one that never gets between a user and their data.
The acquisition of Mailbox is a great move assuming they bolt Mailbox on-top of Dropbox.
What I would like to see is API integrations across services such that I can eventually store all MY data in MY account and allow other services access to it.
This could cause an issue for some services - but the fact is that I don't want to host all my mail with gmail, all my pics in FB, etc...
I want a storage glob and a set structure for "pics go here" "docs go here" "mail goes here" and a range of apps that access the data in an authorized, yet ad-hoc manner - but at the end of the day, the data is MINE.