And I can see why. With no tactile bumps, the second screen is not a dedicated keyboard. It is just that, a second screen. As far as typing, it does not provide anything extra that a larger single screen would not. With all the disadvantages of no support for two screens that you mention.

No, what I had in mind is a keyboard with software reconfigurable key labels. The fact that it is done by hiding a screen under transparent pads is a technical detail that the users would not need to know or care about.