Unfortunately, it's on the editor to support mixing fonts. There's never been multiple compatible monospaced fonts before so no editors really support this yet. Lots of editors also don't support variable typefaces properly yet (ahem, VS Code) but this is going to change.
Ultimately what you're describing is the future! But we have to release the typefaces to bootstrap that future.
We made a prototype extension that hack it into VS Code. But they're hacky af and not really releasable.
To expand on this, Emacs uses a system called "faces" to draw different textual elements, for example font-lock-comment-face to draw comments. Faces can have different attributes, like font family, foreground colour, background colour, having a box around it,...
So if I want to use a variable pitch font (like say... DejaVu Sans) to draw comments, I can set the font-lock-comment-face to use the "DejaVu Sans" family.
Do you know of any Linux terminal (eg. xterm, gnome-terminal, etc.) that would support multiple fonts? I'm intrigued, shouldn't be very hard to add support to command-line programs (once terminals supported it).
Unfortunately, it's on the editor to support mixing fonts. There's never been multiple compatible monospaced fonts before so no editors really support this yet. Lots of editors also don't support variable typefaces properly yet (ahem, VS Code) but this is going to change.
Ultimately what you're describing is the future! But we have to release the typefaces to bootstrap that future.
We made a prototype extension that hack it into VS Code. But they're hacky af and not really releasable.