This is already possible in MM5 (Drop Box, One Drive, Google Drive), MM5 is in alfa state: http://www.mediamonkey.com/forum/viewforum.php?f=29 (keep it mind it is an alfa -- i.e. many features are incomplete and haven't been thoroughly tested).

I'd love the ability to sync to or copy to some of the cloud based services. In particular (because I use it ) Amazon Music would be great. Particularly given the fact that you already have the links to the sites through the app.

Right click send to cloud would be epic.