For a Linux user, you 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. [1]
Other options like OneDrive don't have such capability on Linux or are not available there at all. It's very hard to find a suitable alternative especially a European one.
But, for anyone on a site literally called "Hacker News", a DIY dropbox should be trivial. The fact that anybody, especially, "nerds" or "hackers" would pay good money for what is effectively an FTP server with file versioning is insane.
I am mostly jealous that I didn't build and sell dropbox. Becoming an overnight millionaire by setting up an FTP server.
But seriously, modern approach, rclone[1] + "cloud" stoage (webdav, ssh, wasabi, whatever)