Yeesh, no. I'm against it. But I do think it is reasonable for a "windows PC" (one where the device is sold with windows preinstalled) only can boot windows by

Yeesh, no. I'm against it. But I do think it is reasonable for a "windows PC" (one where the device is sold with windows preinstalled) only can boot windows by default. As that is what will benefit the absolute vast majority of users (though to be fair, there is plenty of lower hanging fruits than the boot process for most users). But it is wholly unreasonable for the owner of the PC not to be able to disable that by themselves (without internet access or anything). If the solution to that is to require a UEFI password to be setup (perhaps windows could set the UEFI-password to the same as the main user if it hadn't already been set) - and resetting the uefi-password would wipe any encryption keys in the TPM that is fine (as long as the option to reset the uefi password exist). And further, not allowing the owner the control to dual-boot windows and any other OS is also wholly unreasonable (but I'm fine with the owner having to enable it in UEFI first).