Moreover, it can actually be at least "more straightforward" to reach accurate wall clock timings with an FPGA, than by trying to meet deadlines in a common OS

Moreover, it can actually be at least "more straightforward" to reach accurate wall clock timings with an FPGA, than by trying to meet deadlines in a common OS environment, as the FPGA is "just" loaded with a bitstream that will it do more or less exactly what the original chip did and nothing else, spoken strictly in the digital domain. I'd also like to think that it's more efficient, since at least in theory it could be (cutting down on all the extremely superfluous software overhead for the task), but sadly I don't actually know how common FPGAs really perform in that specific case against reasonably efficient modern CPUs.