Can't all modern Android tablets connect to all modern peripherals? The first one to ever exist (Xoom) can connect to a display, wireless keyboard, and can act as a USB host to connect to arbitrary USB devices. I imagine the most recent tablets are far more advanced in that area already.

Connecting to peripherals is irrelevant in the tablet takeover. In fact, tablets are irrelevant in the tablet takeover. What's going to happen is that the tablet OS and app ecosystem will reign while the form factor becomes whatever is convenient for the task at hand.

Media consumption? Tablet. Work? Unknown form factor, but with correct input/output attached and running the same software as the media tablet.