How could certificates ever work in embedded applications connected to consumer LANs that provide interfaces over HTTP? Aren't certificates tied to IP addresses, which wouldn't work with e.g. DHCP? Not to mention certificate expiration and updates…
On a manged corporate intranet, Active Directory can push out a new CA and your computer trust whatever certs the local IT department wants to cook up, but it breaks down with a BYOD office or SOHO lan.
I manage a few intranet websites, this encryption requirement basically kills any interest I had in experimenting with HTTP/2 which was already miniscule. I'm not seeing the use case for HTTP/2 unless you're already all-https or in the Top N websites and want to slim down bandwidth use.
Generally the devices just generate a self-signed certificate and you have to click through the warning.
I don't have any problems with the campaigns to make the public internet HTTPS-only. However, for software inside an intranet, or software that just wants to expose an interface on http://127.0.0.1:*someport* non-SSL is the better default.
If people want to protect their intranet that's great, but it means that they have to go through the work of buying a cert, since only they know the hostname it will be exposed as. That's a poor initial-install experience.
Nowadays, I'm a firm believer in "encrypt all the things", but that's because I'm a geek and can deal with the PITA. There needs to be either an encryption mechanism that's completely separate from authentication, or the use case of LAN encryption for regular people needs to be addressed in some other way.
No, just to domains.