I would say that Motorola was simply ahead of it's time. The cpu on my Atrix was honestly just a bit too slow to smoothly browse the web and do stuff. Motorola should be acknowledged for their innovation & proof-of-concept.
There's been a few all right. I remember the Celio Redfly for one. None of them worked so well.
That said, tablets didn't work so well when Microsoft tried them out 15 years ago, but they blew up later. Same with a number of other techs that weren't ready. Is this the time for smartphone computers? Nah, but keep an open mind!
I currently carry around a bluetooth keyboard and have to awkwardly use it on the train etc, with my phone at awkward angles. I would absolutely get this if it were production ready.