Similarly, Basilisk II is a very worthy emulator for Mac 68k emulation so there's a lot to draw on for QEMU and the like.
In my QEMU fork there is support for a 68000 virt machine so you can have a multi-ghz emulated 68000 with 128MB RAM (maybe more, haven't tested) if you really want that.
N.B. The Author of Chip4Mac68000 has been planning a port of uClinux in the future with his SDK which explicitly avoids using the Macintosh ROM at all, running bare metal directly on the hardware. Might be worth taking a look at if you're unfamiliar.
I'm going to do a u-boot port for the Mac at some point. It'll use the ROM to get loaded and then get rid of it. That'll work on nommu and mmu Macs and make the modern linux on Mac experience a bit nicer.
There have been variants of the kernel around for some time that can run on microcontrollers without an MMU (mainly uCLinux).
Of course the 2.5 line was the unstable pre-release for the 2.6 kernel. That means that stable mainline linux has had nommu since 2.6.0, which was released 17 December 2003.
So yes, some time indeed.