One thing is that context switches have become less of a problem with the advent of multicore systems. But we are not at a place where you can have your dedicated filesystem core for each filesystem, so they are still relevant.

And yes, CPUs are generally optimized not for context switches, but for numerics and certain single-application benchmarks. So computations without any context switches are very fast. Application to Kernel switches are somewhat fast as well. But application-to-application or even worse application-kernel-privilegedFSprocess-kernel-application will be slow as hell, because those numbers never make it to the TOP500 or benchmark sites.

Context switches also have already been optimized too much, Spectre and Meltdown in all their variants are a certain kind of botched context switch. That means that certain optimizations are now out of the question, context switches will be optimized more carefully (if at all) in the future. So there isn't too much hope for a faster but still secure context switch.

I think the actual future in a decade or so will rather have more cores, less context switches and a more computer-network-like CPU. You will have your filesystem server process on the filesystem/disk-IO core and you will speak some filesystem protocol via shared memory over a on-CPU network.