Nothing says maturity or intelligence than claiming that the same universal, high-power, high-I/O port for charging, data, and video can done from a single USB-C port to a nice 5K display with its own USB-C hub built into the back is an "octopus." How miserable it must be to be able to have one plug that everyone can use. It's amazing you ever moved on from VGA, serial and parallel ports.
You're not making it any better. You're not even describing a realistic scenario. We (myself included) already have our equipment, external displays and workflow. SD, HDMI and TB2 connectors are anything but "legacy" in 2016. Colleagues use SD storage extensions. Your "solution" would be to additionally buy the LG 5K display (which Apple didn't even bother to make and market for itself) as well as complete peripheral replacements and/or dongles/USBC hubs. Brilliant. Does it come with a complementary 10K donation?
How is it "one cable everyone can use" when noone has it out of the box? Even a new iPhone 7 user cannot plug their phone to a new MacBook for crying out loud.