With its limited pin count, it's not a surprise that the Lightning connector does not have the bandwidth to transfer uncompressed video.
I totally disagree. Coax and Ethernet get you plenty of bandwidth on fewer pins. When Apple announced this thing, I was delighted that they must have some kind of brilliant plan for using these very few pins in a flexible, high quality, eventually low-cost manner. If their plan for flexibility was just "send a system image over USB, then connect via USB to that thing once it boots" then I am surprised and disappointed.
Costs may come down as we approach computing ubiquity, but this puts a ceiling on quality and that seems like a poor plan. We might want our iPads to drive 4K displays. Probably not next year, but in 8 years, sure.
I'm sure there are real, physical limitations that I don't understand that make this required, but I'm still disappointed.