Apple already sells an $80 adapter hub for the rMB. If you read the reviews, you'll see that it barely works. USB hard drives that require power won't work. As soon as the MacBook is unplugged, any USB devices stop charging. And worst of all, HDMI doesn't work properly for many people because it can only push 1080p at 30Hz. What?? Even worse, OS X is so locked down that it often won't accept anything other than the default resolution of attached monitors, which -- if it's 60hz, means HDMI won't work at all.
That cannot happen in a Pro laptop.
You won't have to worry about any of that with the rMBP's.
Iris 580 is more than powerful enough to be paired to a highres&high framerate monitor. + TB3 will also be able to pass through immense power.
The only problem people could run into is if OSX doesn't support a certain monitor/driver/resolution. (Which is usually rare)
[doublepost=1459350267][/doublepost]To calm all the heat that's been in these past few pages, here's a classical music piece I discovered yesterday. Highly suggest listening:
https://soundcloud.com/beshevli/ilya-beshevli-wanderer
A caresse to the ears.