I've read them — but the important factor is that Linux with KPTI is now doing a full context switch between userland and kernel, which is the same cost as switching to another userland process to handle the syscall (which is exactly what a naive microkernel would do).

I've always been a proponent of microkernels, and this is another situation that might help with this.

(Personally, I've been affected by the failures of monolithic kernels way too often. When a simple OpenGL or WebGL program manages to hang your GPU driver, parts of the kernel, and all DMA operations in the kernel, and your system becomes unusable, then reasonable isolation would be preferable)