If OS4 was released for x86 but MorphOS wasn't, then I might be tempted to buy a copy if it was cheap enough.
I lost all interest in OS 4 when I bought a MorphOS license for my eMac. Of there had been a hw solution for OS 4 for a similar price as what I got that eMac for earlier I probably would have bought an OS 4 license. I can see going for one or the other, would there be any good reason to have both?