The dual CPU 2.5 and 2.7 are liquid-cooled and so are all PCIe/dual-core G5 (the Quad has 2 dual-core G5 and is a wet as it gets).
The fastest air-cooled is the dual CPU 2.3 GHz (not to be mistaken with the dual-core at 2.3GHz).
Putting an air-cooler into an unit designed for LCS might work ..... for a moment .... (aka really stupid idea),
I'd say anything with an AGP-Slot does have a realistic chance for MorphOS, those with PCIe not in the forseeable future.
But as allways, wait till offcial announcement before buying HW