What problem is being solved here? Insufficiently cute links? I mean, I agree with you that
talk.extremely-long-domain-name.online/t/slug/1234
is generally inferior to
talk.web.it/t/slug/1234
… but the solution to that is to prefer a shorter (within reason, and finances of course) domain name?
Plus, you can already “shorten” any Discourse link (to a topic) by doing
https://meta.discourse.org/t/-/15339
versus
https://meta.discourse.org/t/how-should-short-links-be-supported-in-discourse/15339