They don't make any new PPC mini's so obviously the available HW decreases day-by-day, hence my comment 
Don't get me wrong though, I've got nothing against MorphOS so respect to the developers if they can port it to new HW platforms 
What does the fact that discontinued Mac hardware availability is constantly decreasing due to eventual hardware failures have to do with MorphOS for the MacMini ever being completed by the MorphOS dev team?
Thousands upon thousands of PPC MacMini's were probably produced, I have not taken the time to research a final number of sales, but I think that the supply of used PPC MacMini's will satisfy the demand from the MorphOS community of, what, 500 to 600 current users and maybe if we are really optomistic, that number could double, or more, with the release of MorphOS on the MacMini and still there would not be a shortage of G4 PPC MacMini computers, unless you think all the old PPC MacMini's are being sent to the trash bin.
I have seen so many people post negative comments about MorphOS being ported to used and discontinued hardware instead of something new, but I vigorously disagree with this sentiment, as I see the MacMini port as the most logical, quick port to do while waiting for better hardware to become available, or to try to gain some additional users and additional performance beyond the Pegasos1&2 and Efika to tide us over until the dev team can complete a port to a better hardware solution (hopefully new hardware that is still available). Given that MorphOS is a PPC OS, it just made sense to port it to another PPC hardware platform and the MacMini gives a performance boost over the Pegasos2, while offering a low cost to find and buy.
