IMO accelerators often leave you with various bottlenecks - for instance, a A1200 fitted with a Blizzard PPC would still have the same old I/O speeds. The 970 would need lots of technology such as DDR RAM, 8x AGP, PCI-X etc to take full advantage of the chip - in the end, what you'd get is a seperate motherboard on top of the A1; wouldn't it be just as easy to have an A2 or whatever?
I'd imagine that accelerators were so popular was as they allow far faster processors while keeping the custom chips and stuff resident on the mobo for apps that need them (ie the OS). With the A1 having no custom components that need to be kept, I personally don't think an accelerator would be much sense.
BTW, I know very little about PC architecture, PPC etc - I could well be wrong, but it's just my opinion.
