There are various hardware singletons that need to be managed for this to work properly. This raises many questions.
Which of the kernel does the PCI enumeration, for instance, and how it is determined which kernel gets ownership over a PCI device? How about ACPI? Serial ports?
How does this architecture transfers ownership over RAM between each kernel, or is it a fixed configuration? How about NUMA-awareness? (Likely you would want to partition systems so that RAM is along with the CPUs of the same NUMA node).
Looks to me that one kernel would need to be have 'hypervisor'-like behavior in order to divvy up resources to other kernels. I think PVM (https://lwn.net/Articles/963718/) would be a preferred solution in this case, because the software stack of managing hypervisor resources can already be reused with it.