I have said it until I am blue in the face that any engineer with a half decent IQ would be building cheap motherboards based on the IBM Xenon 3.2Ghz CPU which is compatible with PowerPC. This CPU is 4+ years old now. They should have made the call to IBM a long time ago at Hyperion/Amiga Inc etc. Given some 50 million IBM Xenon CPUs have been fabricated they could probably sell them at LESS than 604e prices charged to Amiga companies.
If only! IBM has been manufacturing the Cell processor, a sucessor to the Cell, and the processor in Microsoft XBOX360 (which you've mentioned) for several years now.
It has been discussed, but IBM qualifies each manufacturer's application for Cell related projects. If it finds merit in the application it will work with the company.
IBM wants to make a profit from it's ventures. So far, the only applications it has allowed for this technology are high volume/ low profit margin products (like the XBOX360 and the PS3) and low volume/high profit items (like Cell based Blade servers).
You can call them if you like. I could even give you the name of the person heading that department (he responded to my own inquiries quite cordially).
However, since what you're talking about looks like a low volume/low profit product, I don't think you'll be able to get approval for it.
I wish I could say that I don't understand the logic in this, but Motorola (who made the last Amiga processors) isn't in that market anymore and IBM still is.
They seem to understand that in order to stay in business you need to do more than create a good product. You have to market it right. Cell based PCs aren't going to happen.