Shrinking the kernel with a hammer

XIP-like ideas are handy on very parallel machines (thinking Xeon Phi-like, but any other single-image box - or rack - with a lot of cores would fit). Knowing a given memory range is immutable after you're up and running would make it easy to use core-local memory without worrying about it being consistent across the whole machine and no need to go across the motherboard-side bus. It's not a problem other cores can't modify your core-local memory because nobody is supposed to do it anyway.

Of course, core-local memory is useful for a whole lot of things besides that, but having to be concerned a process stays local to a specific core makes everything more complicated. If all cores have duplicates of frequently code memory that can be read faster than the main system memory can, all cores can spend less time memory-starved.