1) Having seen this in the past, I am wondering how many UEFI's will be shipped with no way to turn off the secureboot. I don't see vendors getting a no you can't if they don't ship it and it will be one less thing for them to have to put in the interface.
2) The push for secure boot will be coming from more than just Microsoft, I expect it will be required for PCI and various other compliances which will mean the majority of systems bought (eg enterprise systems) will require it. That will shift the systems that do not have security boot to being a very very small minority if at all.
3) My limited understanding is that the cost for designing any motherboard is in the 10-100k range these days depending on the things people want on the board (and all the patent licenses, cross licenses, etc needed).
4) What of the other commercial vendors? What are their plans when dealing with the first two above?