As I noted on en.Wikipedia in July 2014(!)
It would be really useful if the pop-up linked to the Wikidata equivalent of an article, displaying the Q value (e.g. Q144 for Dog) as the link text.
Having this feature would significantly increase my productivity, in certain regular tasks.
Specifically, I need to be able to right click and "copy link text", to capture the ID, so displaying the value as the (whole) link text, rather than text such as "visit Wikidata", is imperative
A mock-up can be seen at https://commons.wikimedia.org/wiki/File:Mockup_of_Wikidata_ID_in_popups.jpg
[I note that I received a reply, then, that this is "abandonware", but noting the request here in case a developer is now/ becomes available]