[whym]

There has been an RFC about it (for years).

"Remove .m. subdomain, serve mobile and desktop variants through the same URL" https://phabricator.wikimedia.org/T214998

[throw0101b]

There problem is when your auto-detection gets it wrong and you keep getting served the mobile version even if you are not (looking at you www.arista.com).

[dspillett]

This is a good use of a session cookie. Or even a stored cookie.

It would be considered a non-tracking essential site function value too, so you wouldn't need to beg permission (contrary to what people who want us to be against privacy legislation will claim), and the site is probably already asking for permission anyway for other reasons so even that point is moot.

[account42]

If you do it right you don't have auto-detection because you don't have separate versions of the page in the first place. CSS is powerful enough to adapt a page to whatever viewport it happens to be displayed on.