Pretty easy to do so - not that many parts!
Not many parts - but pretty tricky for the 6 layer PCB with blind micro vias to get all the HD interconnects.
If you've not already seen I'd recommend a read of:
http://www.wired.com/opinion/2012/09/ra ... -sell-out/
It's possible to make a Raspberry Pi compatible, but the cost saving would be fairly small to the end user so unlikely to make sufficient sales - why save £3 on a "rip-off" when the real thing is only £30.
A more practical thing would be to create a more specific version for a specific commercial project dropping any superfluous components. But then if you have the capability to design the PCB required you probably don't need to copy the design from the Raspberry Pi (thinking of dedicated Linux based machines already on the market - set-top-boxes / NAS / Routers etc.)
Being able to see the Schematic can have advantages and whilst it's possible to work it out from the description of the changes it easier to see directly on the diagram.
AFAIK there is no updated schematic publicly available yet.
I find the schematic to be quite useful. It's been interesting to see where the fuses are in relation to the various connectors - eg. micro-USB before 1.1A fuse; GPIO after that fuse; USB through the 140mA fuses (early versions only), therefore you can see that if you try and power external components through from the GPIO (using micro-USB as source) then you are still limited to 1.1A - whereas if you apply your own power source to an external circuit and feed that supply back to the Pi then you can overcome that limitation.