Wikibase currently uses the /wiki/Special:EntityData/ path for canonical data URIs.
We should switch to using the new /data/ path for this purpose.
/data/ is currently implemented by rewriting to /wiki/Special:PageData/, which redirects to /w/index.php?action=raw. Wikibase intentionally does not support action=raw. For Wikibase, we would probably want to hook into Special:PageData and make it redirect to Special:EntityData (not to be confused with Special:EntityPage - yay, name confusion)