The trend of multicore and NUMA means that hardware increasingly looks like a traditional network of many separate computers. The natural conclusions of single-core scaled up to, say, 4 cores, shift when there are 8+ cores. Locality becomes crucial; just as you wouldn't split up data-path dependencies across LANs, you shouldn't split them up across NUMA sockets either. Ignoring arguments about locking, message passing, cache management, and whatever, the most pressing argument for multikernels (or at least, far increased per-core state and reduced shared state) is that locality is essential for performance.