This isn't streaming, its the last 50cm from your computer to your display. The 200 times more of data are already handled without a sweat by today's interfaces. Dual link DVI, from 1999, can already do more than 1080p.
Apple are trying to handle all technologies without custom hardware in the device. Effectively, they have turned it into a streaming scenario. It's not as weird as you'd think -- there are USB3 video adapters that work the same way.
DVI, HDMI and MHL all require custom hardware in the device. As the Apple engineer said, Apple are trying to avoid this.
Taking 1 master protocol (DisplayPort) and converting appropriately would make a hell of a lot more sense then starting with your own proprietary format, and putting compressed video decoders in your cables.
Avoiding custom hardware in devices just seems ridiculous - to support new standards Apple are either going to have to update their chips or update their devices, and they will have to update the cables too. There's not a saving here that isn't achieved by simply using an existing standard.
Sorry but are you talking about the right connector here ? Lightning is for the iPod, iPhone and iPad.
Of course dual link DVI et al can do more than 1080p. They are all huge. Apple's needs to support not just today's thin devices but those for the next decade (iWatch ?).
