Maybe that's a stretch but...Could that coprocessor be a GPU? HTX
video card, anyone? With truckloads of bandwidth to CPU and main
memory, and no extra latency that it is otherwise inevitably
introduced by any intermediate components (PCIe bus, PCIe controller,
and the chipset as a whole).
It's possible, yes. However, as with most things, there probably
isn't much point in doing so. Video cards are quite bandwidth
intensive, particularly when compared to most other devices in PCs,
but not all that dependant on low latency. With PCI-E 16x they have
the same sort of bandwidth that Hypertransport, in it's current
incarnation, provides already and future higher-bandwidth versions
aren't likely to produce much of a performance boost (really we
haven't seen too much of an improvement since the bandwidth figures of
AGP 2x).
The problem is simply that if a video card has to go off-card for
memory access, it's going to be VERY slow in terms of both bandwidth
and latency, regardless of what sort of interface you use. An extra
couple of gigabytes/second or a few nanoseconds less latency isn't
going to help matters much, it's still REAL slow as compared to the
25GB/s+ bandwidth and extremely low latency of on-card memory.
So basically while an HTX video card is certainly possible, it would
probably only buy you about 1% over PCI-E 16x, it would cost a lot
more to develop and it would only be usable by a VERY small number of
users. Even if all AMD-based systems came with HTX slots you would
still only be looking at ~20% of the market, probably not worthwhile.