I'm already using the Unicode block range, and a little from the symbols, geometry, math and braille ranges. You can turn ranges on/off and combine them in different ways.
There's ASCII too in some of the examples because I think it works pretty well as a complement to blocks, when used for dithering only (--fill ascii).
I'm always looking for more Unicode symbols to put to use, though. I think PETSCII and Teletext symbols are supposed to make it into the standard soon, if they haven't already.
Edit: Forgot to mention TV looks very good, an actual useful tool for big geo images.
This is great, I've been working on something that tries to do something similar among other things. ANSI's going to come back in a big way - I got a hunch!
Here's what I made, but I'm keeping it stealth this month. I did make an editor/Converter, it's not great, but it makes ANSI's, and 256 colors as well. It's what I did with those ANSI's that's interesting - I stored them in the blockchain as non-fungible and created a neural network based off them. It's done, it's coming. Just don't want it all to come too fast.
ANSI X3.64 plus almost 30* years of oddball extensions. For a long time, "ANSI codes" or even just "ANSI" was almost synonymous with that (increasingly loosely defined) standard, at least in the context of terminal graphics.
Now I'm not sure that still holds, but I decided the post title didn't need to be even longer and more arcane :)
https://trixter.oldskool.org/2015/04/07/8088-mph-we-break-al...
Explanation & pictures of how some of the techniques work:
https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-...