Point is, you don't need Obsidian (or all of its plugin). People have been making do with Dropbox and plain text (.txt) files perfectly fine for years.
Wow I never knew I "can already build such a system yourself quite trivially by getting an FTP account, mounting it locally with curlftpfs, and then using SVN or CVS on the mounted filesystem".
Plain-text folder on a cloud sharing service. Edit with notepad.exe or whatever editor you prefer. Others have been doing it with .doc files forever, or .rtf.
This is why people use Obsidian.