On enwiki, an admin was able to create a filter that would block autopromotion.
While admins do have abusefilter-modify-restricted rights, the ability to block autopromotion doesn't appear to be enabled on enwiki.
Tested on enwikiversity, which has no restricted actions enabled - was able to block autopromotion as well, but neither block nor rangeblock.
 See filter history and noticeboard discussion
 See that enwiki doesn't enable it
 See https://en.wikiversity.org/wiki/Special:AbuseFilter/history/20