Early qemu versions had problems with the NeXTstep PS/2 mouse drivers. I created some patches for ancient qemu versions (0.8 and 0.9 in 2005...) to emulate a Microsoft bus mouse, which worked well with NeXTstep (https://github.com/michaelengel/qemuNextSTEPpatches).

I haven't tried running NeXTstep in qemu recently, but I suspect it might simply work today.

The Previous emulator for "real" black 68k-based hardware that is mentioned briefly in the article is actually much more fun and also allows you to run 68k-only software such as Lotus Improv - http://previous.unixdude.net