I feel like these are the only things worth upgrading even in a desktop too. Unless you are the kind of person who buys the new CPU every year, upgrading anything in a desktop usually means replacing almost everything.

Every time I've looked at upgrading a part in my PC it's been the case where the CPU socket has changed, memory has changed to the next number of DDR, etc so it's basically just buying a new one of everything but the storage, psu, and case.

There are absolutely cases where I've wished I could upgrade the storage in devices though.

No, not really. I bought my current motherboard in 2018, and it's still more than good enough - runs almost everything at max detail 1080p/1440p - after I replaced the CPU+GPU 2 years ago.

Upgrading, yes, but sometimes one of those parts breaks and it is nice to be able to fix the machine with the cost of just that one part.

Valve's already said they hope to extend their relationship with ifixit to allow parts to be purchased, so that would presumably cover this kind of situation.