This subthread is strictly about web serving. Requirements combinations like "HTTPS serving in pre-init or board-support code" or "real-time HTTPS serving in under-powered embedded board" are not practical or relevant, unless we replace "HTTPS serving" with something else.
With regard to the other point, if we are using a memory-safe language, then we can use fork to get an instant arena, regardless of how that language performs resource management under the hood. Whatever allocations happen in the request, of memory or file descriptors, are reliably gone when that exits. If there is any problem in the implementation of the memory safety, the failure is contained to a process. Thus we have an additional reason to use process containment: not having control over the memory management, and not trusting it 100%.
As I said, if you can fork all the time you probably shouldn't be using a memory-unsafe language anyway. Nothing you've said so far has suggested otherwise. The basic techniques for implementing your own memory safety are still valuable and worth discussing for people who aren't in Easy Mode all the time.