I think you're wrong. Everything in history to date with semis has been focused towards integrating more on chip, or at the very worst, on package. This puts the memory as close as it can get to the chip without driving the chip's cost up astronomically. There's absolutely nothing to suggest they'll de-integrate moving forward.
The biggest problem after this is how much the GPU and CPU have to fight over main system memory, which really brings us to the end game of GPUs altogether. Sooner or later there won't be room enough for both in the picture, your single heterogeneous core or MCM will have both a CPU and GPU on it (and probably a half a dozen or more application-specific accelerators).
I wasn't suggesting there would be any disintegration. Just that off substrate memory will be reintroduced in-addition to HBM.
If you need a point of reference take a look at L2 cache. It was originally chips on the motherboard, then with the PII it was put on a Processor Card, then with the PIII it was eventually integrated into the Die.
