I started working on this feature about a month ago: https://github.com/snizovtsev/tmux (it's in early experiments, not ready for a try).
Luckily tmux has a well-established "control mode" protocol designed for iTerm2 that can serialize internal state updates into a stream of text messages. So I do write client-side of this feature right inside tmux.
When it's ready, you will able to embed remote sessions inside local tmux instance by calling something like "ssh example.com tmux -CC attach". It will auto-detect "control mode" escape sequence and create special "remote session" you can switch into.
If you are interested, connect with me (snizovtsev@gmail.com) so I will notify when feature is ready and ask for early testing before making upstream proposal.
