Support for existing cloud services
Support for using already existing cloud services (dropbox, google drive ...). Then both computers don't have to be online when syncing, and you'll never have to think of syncing manually.
Perhaps it could build upon the existing sync. function in mnemosyne, instead of syncing directly to another computer, pull the data from an folder. Check the folder each time mnemosyne starts, update the folder when mnemosyne quits.