Minerva has been available as a desktop skin available on Special:Preferences for some time, however it has had a hard dependency on the MobileFrontend extension due to its history - originally being part of the MobileFrontend extension.
Thanks to much of the work inside Advanced Mobile Contributions https://www.mediawiki.org/wiki/Reading/Web/Advanced_mobile_contributions the Minerva skin now has a soft dependency on MobileFrontend and will not run MobileFrontend code if its not installed.
When operating in this mode, Minerva will operate in a simplified mode that operates similar to the other skins Vector and Timeless. It will use jQuery autocomplete for search and the watchstar code that lives in core. Features such as reference popups, red link confirmation and overlays for talk and languages will fall back to links.
The code for this change rolls out this week. The new code should only be triggered on instances where MobileFrontend is not installed so should not impact any wikis e.g. Wikimedia production.
This mode will not be enabled in any Wikimedia wikis, but my hope is that it will help improve the skin architecture going into the Desktop improvements http://mediawiki.org/wiki/Desktop%20improvementsproject which will be targeting the Vector experience.
My hope is this project will allow us to apply the lessons we have learned in Minerva to more generalised solutions that work on traditional skins as well and will encourage editors to improve the many templates that are not compatible with skins like Minerva and Timeless when they operate in responsive mode (some of which are slowly being collected in https://en.wikipedia.org/wiki/Category:Templates_that_are_not_mobile_friendl... ).
You can help this effort by installing Minerva on your local wikis and/or using Minerva as a desktop skin on production wikis where it's available and reporting bugs as and when you find them. If you haven't used Minerva skin on desktop in some time, I urge you to give a try. You will likely be surprised by what you find.
If you are actively developing Wikimedia extensions but do not test regularly with MobileFrontend, please do add Minerva as one of your test skins, however please note that MobileFrontend does alter behaviour of all skins (Vector for example ships additional responsive styles), so testing on Minerva without MobileFrontend is not a sufficient substitute for testing on Wikimedia's production wikis.
You can read more about the work that got us here at https://phabricator.wikimedia.org/T171000
Thanks for your time!