You could still do map-reduce operations, but for it to really fly, what you'd want is a side channel between the memory chips that allows the reduce to happen out of band from the front-side bus and the reduction to be sent to the CPU. And any workflow where you can stream the reduction to the CPU that would be even better for latency.

That really doesn't make sense because your system is already using memory that needs to be physically contiguous but mapped virtually. Also, would you say pinned memory is not part of the virtual memory system??

You're only restricted by the fragmentation of the system memory which is an issue yes, but it's dealt with in other ways.

And the security folks will have tons of fun with this enormously leaky abstraction too.

Linux has been dealing with this kind of thing for over a decade now. Specialized SoCs love their memory carveouts.