I only had a quick glance at the source code and my Go is terrible so forgive me if I've misunderstood something. But am I right in the assumption that this includes a proxy that acts as a sort of "middleware" layer for the terminal without explicit support from either the shell or the terminal? If so, this might have a lot more potential than it seems. Imagine how much you could do with "terminal middleware"!
Terminal middleware already exists - screen and tmux seem to be the most popular here.
Imagine you had a framework that lets you write scripts to intercept and modify I/O from programs running in a shell. You could have password managers that automatically (or semi-automatically) answer sudo prompts. Or filters that censor certain strings (if you're live streaming coding sessions this could be very useful) before they appear on screen.
Another useful "terminal middleware" layer could be pre-processing commands before (or after) the shell parses them. You could wrap every command in a `script -c` invocation in order to capture the output so that you can later re-use it without having to redo the processing. (This is probably my biggest pet peeve with Un*x since it really adds up over time.)