Captive portal popup seems like an obvious UX improvement for 99% of people. I wonder how many people on HN even know how to trigger it if the browser didn't try to do it for you.
Update checking and over the air updates make obvious sense to me given that my mother and girlfriend will click "Remind me tomorrow" for years on the macOS update popup, and there's nothing user-friendly about making it so easy for users use old browser versions.
The rare user can turn both off if they want, so what's the big deal?
For anyone wondering: Just try and open literally any http page (note: no s). I use groklaw.net.
There's still neverssl.com, but with the most popular pages using HSTS like Google Facebook and Reddit, captive portal detection is essential for your average user.
Although I wish the IETF would make a standard for doing this at the network level as part of DHCP rather than the current ridiculousness we have. Captive portals are just the buggiest shit.