moving the monitor window (rendered video preview) to
the touchpad area might change that considerably
I'm also up for dual display laptops where the clamshell of a laptop is two touchscreens. It would help water proof the device, simplify the mechanics (lower cost?), give options for keyboard layout (improved ergonomics?) increase full screen size when fully unfolded and might be more comfortable than the stiff keys on the latest gen of MBP. I use an external keyboard when I'm at my desk and want a tactile full size keyboard, so I wouldn't be stuck with only glass.
It costs additional power (with no clear benefit).
Its another point of failure.
It has a big learning curve.
It requires one to look away from the screen (pro users needn't to look at their keyboard).
It replaced something which worked very well: esc key and function keys (who also had F-keys with "fn" combo).
IMO it is an interesting usability concept from an R&D PoV, but not something to be shoved in the throat of users. Unfortunately, Apple decided it is the way forward for MBP users with no option to turn back except for legacy products or switching ship.
I'd be surprised if something didn't exist for Android tablets. But if you have an old laptop laying around, maybe throw w10 on it and see if it works?
On the other hand, you can use something like Synergy, but that's not quite the same thing.
Clearly it will appeal to gadgeteers (as much as I expect the touchbar does) who can use it for instrumentation or other generally distracting applications. Then there is the blindingly obvious: video editing on a laptop always sucks, there is never enough screen space. But moving the monitor window (rendered video preview) to the touchpad area might change that considerably -- it amounts to a 25% increase in display area, and in a 'natural application' of video editing, the monitor would be separate anyway.
I think this design, simply by virtue of being optional, and large and rectangular, is hugely more applicable than the touchbar.
The modality (pumping F6 to enable/disable) could definitely be improved upon. I can imagine it quite natural to use a hot corner of the pad itself as a toggle, or perhaps some gesture or similar.
Very excited to see how these work out in the real world