It been some time since at the session about interoperability of events in the Fediverse as 2026 FOSDEM there was quite consent to move attendance out of FEP-8a8e. I just published a first draft on an additional FEP on SocialHub to catch some early reviews, before submitting it to Codeberg. https://socialhub.activitypub.rocks/t/fep-1cbd-event-attendance-and-attendee-collections/8996