Eh, I wrote it badly :) I wanted to mean that 5-10 years down the road, you're a bit better off having a Skylake GPU than a Broadwell GPU, for driver support/features.
I believe PCIe still has some life left - PCIe 4.0.
You're probably right in some way but this is the death of the PC as an open platform : you would only buy Intel stuff that only works with Intel stuff, AMD stuff that only works with AMD stuff (already that way with motherboard chipsets, but you still have additional controllers) or the third party hardware would have to be made for the specific platorm. Like 25 years ago with a card for Amiga, a card for Mac, a card for IBM PS/2..
You can go check the Intel Purley platform : multi-socket Skylake (both -EP and -EX). It's like your idea!, but with multiple "regular" CPU socket. Very high end, what with six channels of ddr4 per socket ; a socket will either take a regular Xeon (just a big core i7), a Xeon Phi which does have HBM or equivalent, or something else.
But if you want a sound card that will go to plain PCIe or USB.
Similar is the NVLink bus (from nvidia) that will link between GPUs, or to IBM Power9 (they call it "CAPI"). Even more expensive (well, IBM POWER8 / POWER9 ought to trickle down so you can get a motherboard made by Tyan, Supermicro etc. instead of buying an IBM computer that costs like a house)
For consumer stuff I will rather expect just a single socket. Most people are interested in a $50-$100 motherboard rather than a $500 one.