There's a X with sixel support: https://github.com/saitoha/xserver-sixel

I played with this before, and I could use X11 within a mlterm terminal.

I should try to recompile it with cosmopolitan to have a single X server binary both for Windows and Linux

That's amazing!

And this is why I'm so interested in Sixel support for the Windows Terminal (https://github.com/microsoft/Terminal/issues/448)

With that and a X server using sixels, there would no longer be a need for something as complex as wslg for most apps: you could just export DISPLAY in your .bashrc, then use one Windows Terminal tab to start X apps, and the other one to display/interact with them.