I don't know about overprinting per se, but you can already use whatever foreground+background colors you want; how much benefit would overprinting be?

This would allow more complex shapes to be drawn by combining multiple glyphs, which would be useful for complex TUI applications (there are only a limited number of box-drawing characters available) Also, this could allow drawing more than two colours per terminal cell.

That's an interesting idea. The closest thing I can think of is using an extended box-drawing font: https://hpjansson.org/blag/2024/01/18/chafa-1-14-all-singing....

That doesn't solve the two-colors-per-cell challenge. But it makes for some very realistic terminal images.

For higher fidelity rendering, I think the next best option is supporting image protocols like sixels or Kitty inline raster images. I'm not sure how overprinting would compare to existing options.

I've just found that Mintty supports this

https://github.com/mintty/mintty/wiki/CtrlSeqs#overstrike

Oh, like making arrows by overlaying - with > or ^ with |. I could see that.