That's not quite what I meant, because these are still just single chip machines. I was specifically thinking of data centre use where more cores are obviously

That's not quite what I meant, because these are still just single chip machines. I was specifically thinking of data centre use where more cores are obviously desirable, and in previous generations multi-chip designs were common e.g. dual-Xenon all the way up to I think quad-Xenon motherboards. With the rise in core counts recently, most designs have gone back to single-CPU motherboards, but I wonder if we'll decide that 64, 128 or whatever cores per chip is enough, and just have more chips on a motherboard instead. Would give more flexibility for upgrades or replacing faulty CPUs, as well as probably being cheaper to make and easier to keep cool. We can already do multiple 40GB/s interconnects from on-chip to outside the PC using PCIe/USB-C 3.2, so that kind of fast bus between separate chips on the same motherboard should be achievable for when you actually need cache sharing, and I suspect that with appropriate core-affinity settings, most jobs don't require all that much shared cache access.