Great idea

It feel like introvert indoctrination ²

I think so. It would likely be fun for many. Test it. You can always pull it later if no one is using it.

Umm .. no ..

maybe you could integrate some from here instead of (or in addition to) rolling your own https://www.extremelyfungible.com

Reddit vibes with demon eyes? No need for me.

Are you asking for nostr as a whole or for amethyst? I'd say go for it if you have original concepts for it. Reddit's is corny asl.

no

You could auto generate a default version from nostr public key

Mii creation was the highlight of the Wii alêost 20 ye r ago, kids and adults still spend time creating their Mii today (on DS and Switch). If you can create a similar avatar system, it would be crazy popular.