One of the reasons why they can do unified memory efficiently is because the CPU/GPU is a single SoC. If you separate them, you end up with a normal PC architecture, with memory having to go through a PCIe bus. This is possible to do with reasonable latency and bandwidth (thanks to CXL), but we haven't seen that in consumer hardware. Even in server space I think only MI300 supports CXL, and even then I don't think it's something AMD particularity promotes.
Personally I think Strix Halo workstations may come with expendable memory, storage and free PCIe slots. But then you have to deal with ROCm...
