So, what should Amiga programmer do? Just wait for AmigaOS4 to be released (or at least some development material for it) doing NOTHING? C'mon...
I'm not 100% sure about this, but Weren't Epic working simultaneously on Macintosh & Amiga version of that particular game, at the same time developing SDL-like a system, that allows game to be compiled either for Macintosh or MorphOS with very minor modifications to source code?
So, if it was that easy, why shouldn't it have been done?
And should AOS4 ever become ready, it shouldn't be that hard to "adapt" that system for it aswell, and (maybe) be able to compile all games ported that far to AOS4 aswell...