While true that you will be able to modify the efilinux code, you won't be able to run the modified version, since it won't be signed, making it a very theoretical sort of open source. That kind of open-source-but-not-really situation is exactly what GPLv3 was trying to prevent.
If you're able to build your own version, you are certainly able to disable secure boot or install your own keys (both of which are mandatory for Intel hardware). The big drawback is that you have to splash out on your own $99 key if you want to distribute your alternative to people who don't want to disable secure boot.
> ...you won't be able to run the modified version...
"Tivoization"[1] is a different problem than "can't run because of [any reason besides the hardware owner doesn't want you to]", unless you're talking about another aspect of v3. For instance anything that is AGPL'd presumably is released without the passwords to the database, which presumably doesn't allow remote connections! Are you saying that doing such is a violation of the A/GPLv3 in either legality or spirit? (And you can't license all the data in your DB--think of all the poor sites storing user passwords in plaintext. Also data licenses are more tricky than software ones, but if code is data and data is code...)
And of course, even with DRM that supposedly makes it so unauthorized code cannot be run, it's more or less really just saying "we make it harder." I've seen a lot of "we got our tivo to run Linux or something else" posts, and the PS3 drama was interesting to watch unfold.
[1] I side with Torvalds with a dislike for this word: "[Stallman] calls it "tivoization", but that's a word he has made up, and a term I find offensive, so I don't choose to use it. It's offensive because Tivo never did anything wrong, and the FSF even acknowledged that. The fact that they do their hardware and have some DRM issues with the content producers and thus want to protect the integrity of that hardware.
"The kernel license covers the kernel. It does not cover boot loaders and hardware, and as far as I'm concerned, people who make their own hardware can design them any which way they want. Whether that means "booting only a specific kernel" or "sharks with lasers", I don't care."
