NeXT mach was a microkernel as well based on CMU’s Mach 2.5 (in the first release) and was in the market in 1988. It was actually fantastic, even when I was running 0.7 of the OS in prerelease at LANL. Hurd started in 1990 so it wasn’t NEW new imho (originally based on Mach 3.0 although NeXT went there too). There are other ideological differences but the core mach microkernel ideology started at CMU in 1985 making microkernels an 80s technology as well.