Or maybe they will launch Win 12 with optional TPM support.
Imho making the OS(es) TPM only cannot be good for their business, many people are still on Win 10 with no intention to switch, since their motheboard does not support TPM and do not want to upgrade PC / waste PCI-E slot on TPM extension.
The the default keys on the hardware, e.g. the keys hardcoded to the motherboard are 95+% of the time only the Microsoft Windows one’s.
Even if the distro maintainers & developers had everything configured by default to be signed which is a pain in the ass without UKI’s, it still requires the user to add new keys manually. Rarely do you have hardware with a key for a Linux distribution, and even if you managed to get hardware that has them, the majority of the time it’s only keys for stuff like RHEL, Ubuntu Enterprise Edition, etc.
That’s generally not possible, but I imagine if the BIOS is Internet capable it could be.
Nope. TPM isn’t required to be able to install the system, only to take advantage of secure boot and security features of the hardware.