[de_keyboard]

Could the "sync" mechanism be provided by iCloud, Dropbox, etc. so long as it's end-to-end encrypted?

Managing a vault server sounds like a pain.

[lxgr]

The advantage of a vault server is that it can rate-limit your login attempts based on your master password in a much better way than layering an encrypted password store on generic cloud/synced storage using modern PAKEs.