Muxin

Multiplexing inputs would allow to have multiple connections going on over a simple pair of streams.

Unrepl multiplexes outputs but leaves input untouched (as it makes the result feels not like repl) and encourages usage of multiple connections.

Still in some environments it's not possible or easy to create new connections. In such envs, the repl should be first upgraded to a multiplexed repl and, after that, multiplexes should be created and upgraded (to unrepl or other) as needed.