Help me understand: each of those dongles for legacy devices will be connected to a cable that otherwise would have been connected to your computer, right? And you suggest "a million dongles", which is, of course, hyperbole, but let's consider that the new MacBook Pros can actually support 4 external docks through 4 cables that could conceivably sport any number of USB, Thunderbolt, ethernet, SD/CF/whatever's next readers, 4 monitors on the 15" (possibly 6), Firewire 800 and eSata, RAIDS, PCIe break out boxes, etc, etc, etc.
All connected at once, with only 4 cables.
Try that on your 2015 MBP! Just how many cables would you have to have hanging off your old MBP to support even 1/4 of what the new MBP can support?
Oh, and all of those complaining about having to bring along dongles have apparently not left their house in the last 5 years. I regularly pack USB A to mini, micro, micro USB 3; thunderbolt; mini display to HDMI; mini display to DVI; mini display to VGA, power; TB to FW 800; a TB to eSata; and my CalDigit TB2 dock (which rocks). And no, the solution is not to put all of those connectors on the side of my computer because most of them I hope not to be using in a year.
Short term pain for HUGE FRICKIN' GAIN is how I see it.