Is "mediaeval" an outdated spelling of "medieval"?

I saw "mediaeval" on a Wikipedia page, and figuring it was a typo, edited it to "medieval", it was reverted as apparently mediaeval is the UK spelling. However, in all the dictionaries I've found from a quick peruse, including those of the UK, they now prefer the medieval spelling.

Is mediaeval still preferred anywhere officially, or is it completely outdated?

Resources I found:

• Oxford Dictionary Online (a UK dictionary) redirects mediaeval to medieval
• Wikitionary includes stats on it
• An old argument on Wikipedia about it

(Routledge 2016 p.121) suggests that spellings using the ae digraph are still favored in some words but are gradually being simplified. The spelling can be simplified because there is no pronunciation difference: the ai/ae diphthong was monophthonged in English hundreds of years ago.

English spelling has many quirks inherited from orthographers who insisted on spellings that reflected origins of words rather than actual pronunciation. See (Algeo & Butcher 2013 p.162). Some spellings even introduced letters that weren't pronounced at the time, such as the “l” in “palm” or “falcon”, that have since become spelling pronunciations.

In the case of mediaeval it seems plausible that the spelling was chosen to reflect the Latin original medium aevum (middle age).