Plenty of data isn't part of the web, so really doesn't belong in browsers. It would also make syncing data across devices more difficult as all devices would n

Plenty of data isn't part of the web, so really doesn't belong in browsers. It would also make syncing data across devices more difficult as all devices would nee to be on at the same time and have sufficient storage capacity. You certainly couldn't store Dropbox-scale data in the current generation of web browsers.