> Trying to boot Linux from a USB stick failed out of the box for no obvious reason, but after further examination the cause became clear - the firmware defaults to not trusting bootloaders or drivers signed with the Microsoft 3rd Party UEFI CA key.
Isn't that precisely what the GP linked to? If it's just a matter of changing a BIOS switch then this is a non-issue imo.
However, navigating the scary BIOS menus, in a foreign language, with technical jargon even I can't always understand (and I do assemble my desktops from parts). Even keeping running Ubuntu (or Fedora or whatever) on a new laptop would probably not happen for many non-technical folks, if this sort of 1990s level dark arts boot time shenanigans were encountered.
At least that's my experience with relatives and friends who need computers for non-technical work or entertainment. Not all, but most have found Linux overall nicer user experience than Windows, so this would be a net negative development. Defaults matter, so this is definitely an issue in my opinion!