Meanwhile, we take it for granted that there is a protocol for audio calls and text messages but not for video calls. I would like to more easily video call people with iPhones, and doing so would be technically possible but I can't because Apple benefits from the network effect. If I were to get an iPhone it would not be because Apple did a better job at creating a video call feature, it will be because people I know have iPhones and I want to call them. This seems like it gives incumbents in the space a large advantage because they can compete on having a user base and not on quality.
Ironically, Apple itself developed such a protocol for events and RSVPs (ICS), at a time when they didn't have market dominance. This caught on and it is great. I can make a calendar event in Google Calendar, Outlook, or Apple Calendar and invite anyone from any of those platforms. They can RSVP and I can track their RSVPs and they can also create events in their systems and invite me. This is the kind of thing I like to encourage where possible.
Technically vCal/iCal/ICS (whichever name you prefer) doesn't actually support RSVPs. It isn't in the standards documents. In ancient Microsoft nomenclature that pseudo-standard (de facto standard) for RSVPs is the "Schedule+ protocol" named after an ancient dead predecessor to Outlook's Calendar which originated it. I don't know what Google or Apple call it, and it is such a weird dance of (usually) auto-deleted email messages, so certainly has room for improvement as a protocol.
It would be neat to encourage a new "modern" standard there. Seems like something more web-based (JSON REST API?) than email-based might be a more "natural" API today. (Maybe Apple Invite can help lead the way, I don't know if that's on their TODO list.)