Before any of this can really happen, manufacturers need to get together and develop a standard for each component:
* The touch-screen, lcd and backlight need standardized connectors.
* Speakers and microphones need an interface that supports sufficient current with minimal noise
* SOCs need a standardize pinout for common components so that sets of commonly un-included component groups can easily be set up off chip without a lot of circuitry while also functioning on chips with the kitchen sink.
--- GPU on one side
--- ram on another
--- power supply and peripheral I/O on another
--- radio comms on another
Or whatever, the important thing is that it can be the same, if you don't include a standard component, just leave off those "pins". There should be a standard interface that could be used for any components that are not on board (or even if the SOC can turn them on/off internally)