It’s already sort of a thing in embedded processors, such as ARM SOCs where RAM is glued to the top of the CPU package (I think the OG Raspberry Pi did that). But current iterations run the CPU way too hot for that to work, so the RAM is separate.
I could maybe see it be a thing in kiosks and other limited purpose devices (smart devices, smart watches, etc), but not for PCs, servers, or even smart phones, where we expect a lot higher memory load/multitasking.