Mach is not a representative proxy for “microkernels” in 2026.The L4 family demonstrated that Mach-like systems were slow because they put too much policy and too many abstractions in the kernel path, not because a minimal protection-domain crossing was intrinsically unaffordable. The article seems to rediscover, in a somewhat Mach/XNU-centered view, pieces of a design space the L4 community has already discovered and used for a long time. IOMMUs can improve the security and deployability of DMA and user-mode drivers, but barely make L4’s already-fast IPC fundamentally faster.