[scjody]

A decentralized approach that doesn't depend on one corporate service remaining profitable (or one nonprofit remaining viable) would be great.

The Zot protocol https://zotlabs.org/page/zotlabs/home can do distributed event invitations but the leading implementation Hubzilla has horrendous UX and an unpalatable (PHP + JQuery) tech stack. I'd love to have time to reimplement it in a more developer and user friendly way - focusing on events only to start with could make this a reasonable task.