Nothing except CPU manufacturer choices. Mac laptops use it and they're consumer products.
People will have to get used to buying a fixed amount of RAM with their CPU but thats unlikely to be a problem.
MacBooks use regular soldered lpddr5(x) RAM. Same RAM as every other laptop manufacturer, they just use more lanes to achieve a higher bandwidth.
> Mac laptops use it and they're consumer products
No, Mac laptops use LPDDR, currently LPDDR5X.
The normal non-tech-savvy person already does this. They simply don't know that their ram is upgradeable or something else breaks first, before having to touch ram.
pretty sure its lpddr not hbm.
Apple's "unified memory" marketing is so strong that even tech literate people seem to have this misconception!
They have managed to pull this sort of thing off many many times. https://en.wikipedia.org/wiki/Reality_distortion_field