I don't think a laptop keyboard would be too challenging, although I could imagine a lot of variation between different systems, but I suspect it boils down to PS/2 in most cases, which is supported on RiscPC, A9 and Iyonix (although not brought out on the board).
The biggest problem remains the video. In theory, you could rehouse a standalone TFT display in a laptop lid, but the physical fit would be challenging to say the least.
The best route might be to wait for something a little bit more suitable from Ad6.
Amd whilst a RiscPC is clearly suitable in terms of CPU for a portable RISC OS machine, and the effort is certainly novel, I can't say that the luggable form factor particularly appeals, personally.