When editing a regular wiki page as an anon, there's a message saying that the IP will be saved and made public. This is important for data protection/transparency, and may even be required by law in some regions.
We need to show such a warning on the wikibase repo too. Perhaps the message could slide in at the top of the page when the user first enters edit mode. There could be a dismiss [x], which would set a cookie to disable the message.
Doesn't work with JS, but hey, nother does editing...