The boards using LPDDR don't have socketed CPUs. Also, every connector is a huge hit to your signal integrity, so one versus two might indeed be a big deal.

And yeah, it can be, but that's how you end up with the far slower regular DDR. Fast, repairable, cheap: pick (at most) two.

Effectively there are no socketed CPUs for laptops, though, for way more than a decade already. Saying that as I'd fully support modular components, as in desktops.