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.

Edit 2: Here's the PETSCII etc. proposal: https://www.unicode.org/L2/L2017/17435r-terminals-prop.pdf

Will be a blast when/if it gets adopted and font support catches up.