> HBM memory is expensive, it requires a huge amount of extra IO on the die and an expensive silicon interposer. And you still need to keep around the old IO for the DDR5 memory. All that drives up costs, for what would still be a mid-range GPU.

It's a product that replaces both a midrange CPU and a midrange GPU, which together have not only all of those costs but also the cost of needing two separate packages -- a CPU package for e.g. AM5 and a PCIe package for the GPU. Putting them together costs less.

> Also, current software and games doesn't know how to deal with two pools of memory that have different performance characteristics, so the hardware would be underutilised.

Except that's exactly what they know how to do, and they do it already. They expect there to be a slower pool of memory on the CPU and a separate faster one on a GPU. The system could expose them to existing applications in the same way -- the fast memory via the iGPU and the slow memory via the CPU. That's just software.

You could even do better if you have e.g. 16GB of fast memory and your game only needs 8GB of VRAM, because then the other 8GB can be used as L4 cache for the CPU and could plausibly fit the entire working set of the game in it while the only thing in DDR5 is the OS and idle background apps.

Meanwhile newer code which is aware of the configuration could make better use of it, e.g. by not having to worry about the cost of "copying" between GPU memory and CPU memory via PCIe since they're actually both directly connected.

> The design which abandons the AM5 socket and switches to using much simpler and cheaper soldered-on gddr6 memory just ends up being cheaper and avoids the thermal and area limitations of the AM5 socket, so it could probably compete with high-end GPUs.

That isn't cheaper, because then 100% of your system memory would have to be GDDR6. In a mid to high end system that's going to be dramatically more expensive than continuing to have a socket with DDR5 memory channels, because you'd have to replace e.g. 64GB of DDR5 and 16GB of GDDR6 with 80GB of GDDR6.

Meanwhile AM5 supports TDPs up to 170W and sTR5 up to 350W. 170W is reasonably sufficient for the combination of a midrange CPU and midrange GPU -- a midrange CPU is typically ~65W and a midrange GPU ~150W, which together hypothetically exceeds 170W, but a workload that simultaneously maxes out the GPU and all cores of the CPU is uncommon. In that rare case you would simply clock them slightly lower. Knocking the TDP of a 65W desktop CPU down to that of a laptop in that rare circumstance would have a relatively minor performance impact:

https://www.anandtech.com/bench/product/2685?vs=2665

350W would be sufficient at the high end for the same reason.

And if they were going to design a new socket (as happens from time to time anyway), they could give "AM6" a larger footprint and higher TDP without omitting the valuable external memory channels.

But creating a new CPU interface is expensive -- all the OEMs have to design new boards. So if your concern is cost then it makes more sense to wait until the next time you were going to do it anyway, e.g. when DDR6 becomes a thing, and do something else in the meantime.