SVG Color Fonts
You have some support for SVG fonts. How much of a stretch would it be to add full-blown SVG color fonts?
:-) So here's the deal. For OTF files, we use another (open source) project called (wait for it) Opentype.js to read and write OTF files. Right now, they don't support... lots of stuff, including Kerning, Ligatures, and Variables and Color etc etc.
The workaround we use is exporting to SVG Font (which is a special subset of SVG) then using some online translator tool to convert SVG Font to OTF. That's how we can get Kern and Ligatures into an OTF designed in Glyphr Studio.
The OTHER other problem is that SVG Font is kind of a dead format, not being updated or maintained any more. So, they may have support for color, just because SVG has support for color. But I would highly doubt SVG Fonts have support for OTF Variables.
Essentially we are waiting for Opentype.js to add features, and when they do, they will also show up in Glyphr Studio.
While you're at it, how about OTFVar?
Actually, i'm not sure! I'll investigate - if it's easy then I can consider adding it, theoretically it shouldn't be that hard.