Alan's comments at AmiWest about new mobo designs were very enlightening. Basically, he believes there is no point changing the design every few months as it will shrink the potential market (people hanging on for the next design) and prevent economies of scale.
New graphics cards, USB2, Firewire, Serial ATA etc could all be achieved using PCI cards + drivers. Perhaps a 3 year mobo cycle would be decent, with yearly updates on processsor cards?
There are only 2 designs needed: desktop ATX (which we have) and small footprint all-in-one jobby for embedded stuff/ lifestyle computer, perhaps shoehorned into a laptop size thing if it fits.
Personally, I'm very happy with my (outdated) A1G3 which runs at 733Mhz. Cant wait to put OS4 on it.