I just built emacs from source, I love emacs, but no, it does not replace tmux; I use tmux to have multiple long lived sessions on a remote machine, so I SSH into something, start up tmux and then kick off a CLI process that will take a long time to finish.
I'm not even remotely interested in installing emacs on several EC2 instances.
Perhaps that would work? It looks like a gigantic pain in the ass, that after several hours of futzing with it one would find that a bastion server in the way fucks it all up, or it somehow gets lost. I have doubts about it's stability.
If that's working for you, good on you, but I still contend that does not replace tmux. Especially if you have peers.
Thank you for showing it to me though!