That last suggestion about integrating it in devices that don't actually have keyboards is a great idea.
I could see these things being useful in "specialty" or "emergency" situations, especially with ersatz "mouse-pad" capability built in.
The device would have to be cheap and small before I would consider it, if I had a tablet, which I don't, and for transportability, flat is much better than cubic.
I bet it would make you very happy to get back to your real keyboard!