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".
This is why people use Obsidian.
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.