Shortening could be done by e.g.:

/e/ for nevent, /p/ for nprofile, etc

Followed by just enough first letters that it's unique.

This works especially well for self hosting because the number of events would be limited (e.g. a whitelist of npubs of yourself and some alt accounts).

A public service could offer this as a SAAS: you get a short URL and (static) server side rendered page for any event/profile you visit, with a cookie to track your balance, NWC or something nuts.