If I were going with a cynical thought, I would think this is a move to get dropbox into government contracts somehow.
This appointment smacks of the corporate-political complex. It's practically inevitable that USG resources will be used in favor of Dropbox's business at some point.
But the thing is, a lot of this stuff works quid pro quo. What might happen is, USG will pay Dropbox a nice penny to use some of its service... aaaaaand in exchange they also set up a deal to snoop on Dropbox users.
(user management, share management, every user having permission to duplicate or destroy all files they can read, inability of admins to fix those changes, no API access for any administrative or reporting feature, inability to control own encryption)