Can you just access /dev/mem or load a kernel module? Is there a SELinux policy stopping that?

If you can do either of those, it should be trivial to get kexec working by just loading it as a module.

As far as I know, yes, it's possible. No SELinux. Kernel is a branch from 4.9.something pretty far off mainline with a few proprietary binary blob modules. As far as I know the real impediment here is lack of demand.