I have seen a touchscreen on a 701. If you use google you can see a battery of mods. To my knowledge, there are already drivers for this touchscreen that you can add to the Kernel and have working with BT3. If you were to set it up with say, a USB keyboard (targus has a great flip open one that looks sweet, too) and remove the keyboard on the pc, yes you could add more, better hardware. However, there is plenty of room inside one of these EEE PCs to add whatever you want. GPS seems to be nice to have (and I will be installing a 701 in my car to have a navigation system, wifi capabilities, and it will be a head unit for my sound system).
So to answer your post, what it seems you want to do can already be done, and it has already been done.