But, Copernicus, don't forget that PCMCIA and its predecessors and successors were used only for adding peripherals. Storage, modems, NICs, card readers... Pretty mjuch what USB is used for nowadays. They were not used for core components like CPU or RAM.

This is not to say that you might not have a barebone module containing basically just the system bus of some sort and swappable modules with CPU+RAM (a single module), modem, WLAN, display, camera... Buth the mechanical constraints like size and durability will get in the way. A LEGO phone will have a hard time competing with a monolith.

I also suspect the innovation cycle, albeit looking promising in theory, will actually be slower than for the monoliths. By the time a new camera comes out as a swappable module, the competition will have made three iterations already.