Didn't Apple and IBM both do this with the old tan boxes in the 80's with 5 1/2 inch floppies. They were pretty much keyboards with the computing guts underneath and an external screen. Now, why did we abandon this design.... Oh, yeah, because if you break a key on the keyboard, you have to replace your computer. Keyboards are $5 and the computer costs 100's. It just doesn't make sense.
If you need portability, then get a laptop.