It might happen anyway, look at the Afterburner card they make for the Mac Pro for instance, which adresses a niche within the Mac Pro niche.
I just don’t know what kind of volumes the Mac Pro has. They sold over 6 million laptops last quarter, and their total Mac volume is probably pretty well established, but I’ve seen no numbers for the Mac Pro specifically.
If it is much less than a hundred thousand systems annually, then the costs look harsh, but I’m not sure that sales actually are that low. I’m not in that market, so I can’t even stick a finger in the wind really. Numbers, anyone?
Architecturally, those might be the most intrigueing systems to speculate about, but on the other hand they are very much boxes bought to do a job. It could be argued that the balancing of feature sets, performance, cost, power draw, material choices and so on that go into making a computer for the general public is more complex. It sure as hell affects more people. In that sense, Apple started in the right end of the spectrum.