It all hinges on whether future high-end ASi chips somehow have the space to connect loads of PCIe lanes. They would be quite a radical departure from M1 chips (and more significantly, from A-series chips).I think we might see ASi GPGPUs using the same heat sinks as the current MPX GPU modules; hence the rumored "same chassis but six slots" ASi Mac Pro...
Not in the market, but I would assume those who are, and need GPU performance, will want to be able to update the GPU without replacing the whole machine, re-paying for the RAM, drives, and CPU cores they don't really want or need to replace, and taking the time to migrate everything to a new box, vs. unplug one GPU, plug in the new GPU.