Well I've read it as he want's a router and Plasma with a waterbase.!!

If your going to take this route then think carefully about design because changing from one to the other won't be simple as just throwing a bed on top, you'll need to consider Spindle and Torch location because as anyone who's built a CNC router will tell you setting the spindle up takes a good while and you won't want to be removing in a hurry, then you have skimming the bed everytime you switch which becomes a pain.
You'll also have to consider the affects of heat throwing the accuracy of the frame and bed out, which for a plasma doesn't really get noticed or matter, but a router will see it easily. Also plasma is messy and abrasive compared to router and they won't sit well together.

Personally IME these type of Combi machines never do anything really well and there's always a compromise. Better building one or the other to be best they can be.