A little digging discovered that the wonderful OpenBSD packetfilter has 'ALTQ' built in and as such supports prioritised queues:
Also for anyone interested (else just terminally bored) as promised some links for running full blown IBM mainframe operating systems on your PC,
Hardware emulation - from a 1970s System/370 to a modern 64bit zSeries :
IBM VM/370 R6 Operating System:
IBM MVS 3.8J Operating System:
Both are operating systems that you can login to and run apps and compile stuff on etc. But with VM each user gets a virtual machine (logically an entire mainframe) and as such can just run apps, or run an entire OS, such as MVS or even another copy of VM (inside which you can again run VM, and inside that…!) Whereas MVS is much more fully featured, and even games exist for it.