@Acill
There was a Mediator HAL for the original MorhOS release. I found MorphOS to be very unstable at the time, simply closing a workbench window would result in a lockup.
That may be because I had a highly patched 3.9 install, rather than a clean 3.1 partition.
I did manage to get Wipeout 2097 run a bit faster than with 3.9/WarpOS, fast enough to make it worthwhile to swap a few libs and startup-sequences in order to boot MOS.
It has unfortunately been reported that this HAL is incompatable with the latest release of MOS for classic.