You'd be much better of running and supporting Linux or some other form of unix on your Mac Mini if you don't like OSX, there's no chance OS4 will be released fully in the future...
The only other OS which I think (hope?) might be released is MorphOS, but i'm skeptical about even that... and even when it is released the license price is extortionate, considering the Euro -> GBP exchange rate is even worse now.
BTW this is coming from the owner of a PPC 1.5ghz G4 Mini, i'd like OS4.x on the Mini as much as the next person but it just isn't going to happen IMHO.
Hyperion would prefer us to buy overpriced underpowered hardware like the Sam440 than port to Efika or Mac Mini and make it accessible for more people... :-(