Obsidian also has a rich plugin ecosystem with lots of open source plugins that are available and serve the same purpose (and you can use gdrive, dropbox, etc too).
It makes sense to me that they released a proprietary privacy and security focused plugin (that is their core business) and they don't want other plugins to be able to arbitrarily change the server that their plugin is pointed at.
Suppose they have a government customer who is using Obsidian Sync and the sync URL can be changed easily via configuration changes -- now the customer believes they are using Obsidian Sync, but actually their data is going somewhere else.
I don't think you would be surprised to find that e.g. a dropbox daemon has protections to make sure it is pointing at dropbox.com. Why would you expect Obsidian to be different?
(disclaimer: I work on a different plugin that adds file sync and collaboration features to Obsidian)
I tried this on a windows laptop and another main machine. I just ended up keeping my iPad nearby.
When I tried to copy my vault off iCloud, the copy failed and two years of notes were permanently lost.
I’m never putting anything of value in iCloud again.
The ipad is the real stick in the mud and I don't want to deal with an icloud staging zone for everything else, or try to get icloud syncing on linux/android.
For that, I use Syncthing [1] in addition to iCloud. It works exceptionally well – I see my edits in real time across different devices.
As a free software enthusiast, this screams "don't invest time in closed ecosystems".