I doubt the entire kernel would - there are low-level, memory-unsafe operations that an operating system performs that Swift _could_ do, but it would be fighting the design of the language and likely not a great trade-off for the kernel developers.

But pieces absolutely could be. The benefit would be compile-time checking for memory safety issues (reducing crashes) and language-level concurrency (fewer race conditions and a much easier path to parallelize single-threaded code for performance).