Nah, you could easily have much more than 10k threads on regular hardware for a long time with the traditional threads.

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)