I was just thinking the exact same thing. For technical and especially non-technical folk, getting a full nextcloud host set up and working is going to take significantly more time than a simple login into 1Password, where it just works.
Box.net supports webdav if that's what you want. I'm not aware of any other big name cloud storage providers that offer support for standard protocols. It's available for free accounts, too. This does mean the files aren't encrypted, however if your vault is encrypted that may not matter to you.
