If you like that font, you could try out the mono version from iA Writer (a famous writing app) which they have released recently, it's based on plex but looks a bit better imo!

https://ia.net/writer/blog/a-typographic-christmas

Agree. It does seem to be in the repo though. You could submit a pull request for additions I suppose.

It get's even better with ligatures for common coding sequences https://github.com/vikky49/patchedFonts-Ligatures

There's a form at http://programmingfonts.org/ask where you could suggest additional fonts to add.

I love Plex Mono also. It is on this site under Plex Mono although the info & download link is wrong.