Nothing you can't already do. It's just buttons with pretty graphics on them. If you want buttons to do "great productivity enhancements" the tech has been available for that on Macs for over a decade. Possibly decades plural; the Mac has had an active extension community for a long time, let alone the official stuff from Apple like AppleTalk, however flawed it may have been.
And there isn't much you can do with the pretty graphics on the buttons that you couldn't already do with pretty graphics on the screen, especially in an era of touchscreens. The whole touchbar strikes me as a demo-feature; demos great, in practice, not especially useful.
They're not just buttons. They are also sliders, pickers and any other GUI elements that you can think of.
They are visual. So you don't have to memorise any key combinations. Also they are context aware. This means you don't have to memorise all those key-context-application combinations.
It is multitouch. You cannot click at two different points on the screen with the touchpad. So this is an improvement over the current input mechanism.
Is touchbar better than touchscreens? Maybe or maybe not. Who knows now. But note that it is not placed on the screen. It is placed near the keyboard, where the other input mechanisms and your fingers normally are.
You don't need to "look down at the keyboard". In a laptop you are already looking there. It's already in your peripheral vision. And if you use an external monitor (but not an external keyboard), you simply don't have to use the touch bar.
I don't understand this negativity on HN. There will be many creative applications for this new input/output method. I'd rather see people brainstorming on all those new possibilities.
And there isn't much you can do with the pretty graphics on the buttons that you couldn't already do with pretty graphics on the screen, especially in an era of touchscreens. The whole touchbar strikes me as a demo-feature; demos great, in practice, not especially useful.