C10k is basically just impractical without reactive / async / coroutines / that style. But with it it's extremely achievable on even midrange consumer hardware depending on the specific workload.
c10k was coined in the last millenium when a brand new PC would have 128 MB of memory and a single core 400 MHz cpu. And people were doing it with async IO, not threads back then. (Around the same time Java people got interested in Volanomark which is a similar thing but with threads - since Java didn't even have nonblocking IO then).
See eg this about 100k+ threads on Linux in 2002: https://lkml.iu.edu/hypermail/linux/kernel/0209.2/1153.html .. which mostly concerns itself with conserving memory address space since they are dealing with the 32-bit 4GB limitation of decades past.
(c10k was also about OS TCP stack limitations that were soon fixed)
It's obsolete not just because of new hardware but because we got better ergonomics for these new programming styles.