I thought the discussion was about self-hosting data, such that the provided free storage limits by Zotero remained sufficient? And for that use case, self-hosted WebDAV storage for file attachments is absolutely fine.

(The poster I was replying to was suggesting that their departmental users would go over their storage limits for metadata alone, even if they used WebDAV for attachments -- but that seems to be incorrect from my own experience, and everything I can find online.)