Hi David,
first of all thanks again for your great contribution.
Maybe this is a good time to announce that we use org-caldav since several weeks together with SoGO.
SoGO does allow syncing of Android devices too (via an App). It syncs full automatically with the Android calendar!
It comes with a nice web-based calendar (better then what Google offers IMHO)
It syncs with Thunderbird/Lightning.
I never tested but they claim iphone and Outlook support as well.
You can host your SoGO instance on your own server.
On top SoGO offers address-book and email capabilities (both syncing and web-apps).
There are minor problems (on the SoGO side) but overall its running perfectly stable for us.
In total, it made me move from Google to my own server, happily knowing that annoyances like personalized Google ads soon become irrelevant for me. ;)
Just to catch the dropouts ;)
Torsten