WebDAV/CalDAv and CardDAV are a minefield for users and devs. I would love to see something new.
There is at least https://jmap.io/spec-calendars.html just adoption is a bit low for now but I hope it will gain more traction the next years.
what you mean? a new http extension to access/author resources?
JMAP[0], which has in-progress specs for calendar and contacts, is supposed to save us. It can't happen soon enough - if it happens at all.
[0] https://jmap.io/spec.html