Mosh is really great for avoiding disconnections and local echo. Lack of SSH agent forwarding was a problem for me as well, but I have found a workaround - I open a separate plain 'ssh -A' connection at the same time when I need my keys. On target machines I have SSH_AUTH_SOCK pointing to the stable well known location, which is a symlink to the unix socket recreated always by the last 'ssh -A' connection on the server. This allows me to use ssh from tmux session connected using mosh.
