There was Netbook and netbook pro, HP Jornada 720 & 728, NEC 900C, Sigmarion 3 and good pile of other arm based HPC's and mini laptops that all would have made super risc os mobile computers. All of which would have made a suitable base for a laptop and all of the above have loads better battery life than any laptop.
Even now with enough work the 900C might still be a good candidate as it has flashrom and can have it's OS and bootloader flashed easilly and there are plenty available second hand.
Though I suppose with the eeepc being so portable (and well priced - I am going to get one when I have the money) that a version of VRPC for the eeepc's flavour of linux might be a very intresting proposition for all us remaining risc os users. VRPC would be great on a stable linux machine esspecially with the boot times and price of this machine.