Effectively what they are saying they want to do is something that Commodore did all those years ago with the Amiga...
Ladies & gentlemen we are heading into the 80's!
I.e. something like this:
http://www.bigbookofamigahardware.com/bboah/product.aspx?id=60
Which updated added a far more powerful Motorola 68020 processor to the A500 & 4Mb of RAM by simply plugging it into the expansion port on the side of the machine. No updates or extra power cords necessary.
I suppose something along similar lines could be used on versions of the XB1 & plugged into an expansion port...
Or maybe they will go Sega's way i.e the Mega CD & 32X...
Nice & easy to do for consumers but damn ugly to look at in both cases!
Perhaps using the KINECT Port? We also have USB 3.0, which is pretty fast. Fast enough to run an "external" GPU/CPU box? The Kinect port would probably be their interface if the original XB1 becomes upgradeable. Another point against any kind of "internal" mods would be the heat dissipation system in the current XB1.
I know MS spent a lot of time designing the XB1 chassis to avoid all the overheating problems of the 360, so I doubt they would attempt to install more powerful and "Hotter" components inside the chassis.