The "tablet keyboard" is of course a rather simple way to make such a flexible keyboard in terms of software. But it wouldn't be an option for me
I prefer mechanical keyboards because I like to "feel" when I press a key. For the same reason I agree that typing on a laser projected one would be terrible. Also, I like wide keyboards with separate numpad, maybe even macro keys as well. Yes, they take a lot of space, but I have the space, and I'd like to use it for lots of keys which are large enough for my clumsy fingers
Just for the fun of it, I played around a bit and made up a design study - see the attachment. It has standard keys, function keys, numpad and 16 macro keys (6 on the left, 6 on the right and 4 above the numpad). (Depending on your keyboard layout, you'll probably see some of your keys are wider / one wide key instead of two small ones - I made them separate, because it depends on the layout which ones are connected.) Of course, each key is supposed to have its own display
Note that I haven't left space for keyboard LEDs, but this is intentional. Why would you need them, if you can just light up the caps, numlock and scrlock keys themselves?
And of course, change the icons on all affected keys (letters, numbers, numpad...) as well. The latter could also happen if you just hold Shift or AltGr pressed, so that the letters would normally be small caps, unless you hold Shift pressed. Yeah, I know, might not be extremely realistic to get something like this done, but at least dreaming should be allowed...