I've written a guide explaining how to use a bash script combined with a rebinding of the q key to have very comfortable detaching/reattaching with cmus, see
https://github.com/cmus/cmus/wiki/detachable-cmus

Please tell me if this is good enough, since implementing this in cmus would be a lot of work :-).

Note: For the above solution to work the screen command must be installed: sudo apt-get install screen