Becoming more common. If you want a thin laptop it isn't going to have a lot of modular components. These days you can expect the drive and battery to be replaceable (after much disassembly). Ram is more and more being soldered on. CPUs certainly so, and GPUs have been soldered for the better part of a decade. The systems that are configurable at the factory are usually the high end, larger, models that have the room for MXM modules and socketed CPUs.
Personally I don't see upgradeable laptops as being strictly necessary. Getting laptop parts is difficult and expensive. Unless you are willing to wait for computers to start being recycled. Then older CPUs and GPUs become available on the used market (usually still expensive) You certainly can't get parts new, only OEMs carry them. Minor exception being a few distributors that sell upgrade kits for their own upgradeable chassis.