You can install OS4 on the Mini's HD but it will wipe out ALL of the existing Mac partitions and you still have to boot from a CD using open firmware. At that point the OS will run nice and fast but there won't be any sound, network or USB support among other things.
I really had hoped this would work for a couple of reasons. The PPC Mini packs a lot of power in to neat little package and is WAY cheaper than a Classic PPC system, or an AOne/Sam setup. IMHO it just isn't worth any more time unless a legal solution is found. No one with the talent to write the rest of the software needed is either willing or able to do the job.
It looks like we'll just have to support Hyperion/Acube the best we can and hope development continues and prices come down. I likes the looks of the new Sam systems but like everything else Amiga they are pretty pricey. They do seem like a better value than an old Classic PPC machine though.
-Jeff