I highly doubt the usb splitter would work, signal doesn't get split without direction from an o/s as far as I'm aware. I stand to be corrected though.
Going off the back of the unit, a video feed would be no issue. It'd need to be a camera that's got a generic a/v output so it'd be a constant feed into the head unit but I'd imagine you'd be able to select this as and when you need it. I also imagine the camera would need a constant power supply...so figuring out if you could go straight from the battery with a cable or if it'd need to come off a splice into the lighter...I dunno, depends on the power it needs I suppose?
Can't see an issue with digital TV...never tried this or read about it though so no idea....good luck, all sounds very swish