So, I did give your thoughts a chance and a bit of hacking (See https://github.com/billiob/terminology/commit/3892e3eb87be33809f0df5d64a167aca8b9ebaa5 ).
I won't finish that as I consider it to be too difficult/impossible to do it correctly.
1/ It is not writing to the terminal's fd as that would create a security issue.
2/ It is only writing text to the terminal, but that might create issues because it moves the cursor and writes stuff that the application underneath does not know about.

I can't help you much here because I'm on holidays and I only have my phone. I'll come back in early September.

I can't help you much here because I'm on holidays and I only have my phone. I'll come back in early September.
You could look into win.c about how the command line is showing up because we'd need something like that.
Also have a look at config.c and options_keys.c to see how key bindings are configured cause they'll be needed too.

Ok, to give some update. Turned out, it's harder than I expected. For starters I decided to solve first this problem https://phab.enlightenment.org/T8154 as it just as important, but seems a bit easier, and should give some insights.

In T6240#139620, @Hi-Angel wrote:

Hey guys, I wanted to take a stab at it, but my question is: is there a way to build terminology separately from the whole enlightenment project? I.e. so I could work just on this feature alone?

That said, any hints on what to look at would be welcome.

Okay, I looked at it: turned out it's a separate from enlightenment project, so git clone https://git.enlightenment.org/apps/terminology.git and then building it was enough.

Hey guys, I wanted to take a stab at it, but my question is: is there a way to build terminology separately from the whole enlightenment project? I.e. so I could work just on this feature alone?

Is there a way to place a feature request bounty on this?