From a developer perspective is secure boot more of a obstacle than really useful. You need to use gummiboot, etc. to terminate the signing in order to use developer kernels without having a bottleneck, that one person in the company that does the signing, in the development process. (I am currently working with an Intel Quark X1020 where secure boot is enforced, it's not really nice)
U-boot is ported and regularly run on the MinnowBoard with an Intel Atom.
Do you speak about tianocore? I don't have much experience with it, can you configure it as well as u-boot and just compile in stuff you need?
Update: If you didn't know, u-boot supports signed images too. So UEFI is not necessary for this.
EDK2 is built for Fedora here. It contains build instructions, link the sources, etc.
http://pkgs.fedoraproject.org/cgit/rpms/edk2.git/
As I say I have no great affection for UEFI. Internally the code is pretty awful. But if you want a standard that works the same across x86 and ARM servers and exists already on those servers, then it's UEFI (I'm aware you can run u-boot on x86, but next to no one actually does that).
BTW UEFI is fully open source as of a few months ago after Microsoft relicensed the FAT driver. So we're just comparing two free software projects with different takes on the booting problem.