Are such machines likely coming?
The downside is obvious: there's no "upgrading" such a thing without replacing the entire CPU.
There are a lot of upsides, though:
* the memory interface can be wiiiiide like on a GPU; anywhere from 128-bits to 512-bits so far
* the memory interface needs less power, because it's only driving signals a couple millimeters instead of across a PCB to DIMMs.
Are they coming? They're already here. Have you taken a look at Apple's M1 and M2?