What makes you think they can't? They have the same target audience, some of the same investors, and are working on the same problem - universal access to one's files.
I'd:
* Rebrand Zumodrive as a future version of Dropbox
* Use Dropbox's syncing model to ensure the local cache is kept up to date to a user-configurable percentage.
This would allow speedy access where the local device has the space, and still allow access where the local device doesn't have the space.
