I noticed that the new 2014line-up of Sony PJseries camcorder have hdmi inputs in the specs.
Is this just affiliated with the projector so you can input something like a tuner or disc/media player and have the camera project the signal OR can another camera be plugged in and the capability to switch as in 2 camera switcher?

From the horses mouth:

The HDMI® multi-terminal allows you to connect external devices that have an HDMI output (smartphones, laptops, tablets, etc.) and use the camcorder’s projector to enjoy other forms of entertainment such as video games and streaming videos from the Internet.

Technically you could input another video camera with hdmi out, clean or with overlays, but as far as switching that would be cumbersome and I'm sure there is a small delay and/or black screen output in between such an action.