In the last spring Alan announced that they (Eyetech and MAI) had a deal which enabled them to use same CPU slot as Apple PowerMac (Apple's ‘Megarray’ CPU socket).
But I'm not sure if it is 100% compatible, because:
"
So for the next version of the AmigaOne, the AmigaOne-XE, we have
borrowed the latest cpu socket technology from Apple in the form of
the purpose-designed `Megarray' socket. This means that we can make
low cost, tightly coupled cpu modules using either G3, G4, dual G4,
(and possibly G5 - but information on the G5 is still very sparce)
technology - for use on the same AmigaOne-XE motherboard. Upgrading
cpu power therefore only needs a simple module exchange. The prototype
socketed AmigaOne-XE board and the associated plug-in G3 and G4
modules have already been built and tested. (written by Alan Redhouse)"
If one might be able to fit third party CPU card .. then I do not know if they need some special support from the OS for every different card.
