Well, Navi31 has 5.3 TB/s bandwith between GCD and MCDs on a regular fiberglass substrate.
And 2.5 TB/s of bandwith are enough for Apple to glue two dies together so the Ultra SKU functions basically as a monolithic chip.
If the latency is low enough this rumor isnt even that unrealistic.
Yes, from a quick look, a bunch support it.
For example the Adata case from yesterday, InWin D5, Corsair 3500X or Asus GT302 all have the appropiate cutouts.
$500 will get you an equivalent R7 7700 + A620i or a 12700 + B760i and a cooler but only PCIe4.
So, nice tech but only really worth it for the initial $400 and if you want those PCIe5 lanes...
Just put some cables on the connector and use it like a regular cable from the PSU.
mITX would be ideal for this as you could use any mainboard with this proprietary GPU.
But what's really needed is an update to the ancient 20 year old PCIe connector, ie like the PECFF spec which supports...
IIRC the only "real" instance was the original one which set everything in motion.
The other few dead CPUs were killed deliberately by Youtubers to recreate the problem.