Google, Microsofts etc. servers could be down for a while (minutes, hours, days) it does not matter EN has to handle this.
No I am not asking to support my own server. I am asking for supporting internet standard allowing a client to access scheduling information on a remote server. Fastmail, Yahoo calendar (based on wiki I have no personal experience), NextCloud (yes could be selfhosted) are using CalDAV.
Agree it will cover the vast majority of users.
But for me it would be nice to see that EN implements common internet standard, not only proprietary solutions of big companies. But I understand. Why they should allocate resources to feature nobody will be using it.