That isn't possible. The whole point of HBM is to practically eliminate chip-to-chip wiring so transmission line effects can be ignored altogether and only bare-bones driver-receivers can be used across the interface for minimal latency and extremely low energy per bit. Once traces are more than ~5mm long at 2GHz, you need all of that controlled impedance goodness that will cause the interface to burn 20X more power and die area. Also, the area directly under CCDs, GCDs, MCDs, etc. is where the BGA balls or LGA pads are, putting chips there is going to be problematic not only for mechanical reasons but also for power delivery with all of the displaced power/ground pads.That's why my proposed solution for stacking is mounting the DRAM or SRAM stacks on the Opposite side of the PCB, directly behind the CPU/GPU.
If by "opposite side of the PCB" you meant going through the socket and motherboard or GPU card, that wouldn't be realistically feasible either when each HBM-like interface would add ~2500 balls or pads (half of which grounds for signal integrity reasons) and you would probably want at least one of those per compute die. Hello LGA/BGA 12000+. I doubt normal PCB materials can reliably accept a ball pitch fine enough to physically manage this.