Not leaving pull requests for over half a decade fixing critical issues with not even bothering to comment on them would probably be a massive advantage over Mosh.
one thing to consider though is how a large download over an ssh tunnel effectively prevents any other connection through the same tunnel from working.
to fix that possibly sshuttle can provide some inspiration. they solved that problem.
sshfs may be tricky, because it could lead to locked/hanging file access that never comes back if the server goes away. i don't know what the best approach here is. maybe some sort of timeouts, or maybe do let it hang but provide diagnostics with a command that can tell you what the status of the mount is, and force an unmount or restart of the connection if the user knows that the server went away.
aside from that it would just be nice if i would not have to manually remount every time the ssh connection drops.
another feature that i wish mosh had is to be able to reconnect to an existing session even with a restarted client. i don't know what it takes to do that. perhaps you need to store the keys that were used last time on disk which could lead to some concerns, but maybe that file on disk can be protected, or maybe that is not even necessary. i can attach to an existing tmux session, so if the mosh session is treated like that, it would work too?