I remember working with canbus when i was doing my electronics a level. Security certainly wasn't a consideration then. 
True, and without any technical knowledge of it I have no idea how easy it would be to implement. It might require routing all the inputs to a converter, running the logic and spitting the instructions without a separate bus. 
The whole attraction of it is that it's a single bus that everything can hang off, though, eliminating the arm-sized wiring looms you get in an Omega. Isolation between the safety critical bits of the bus and the eye candy would be a start. Then again, what do you isolate it with? Some sort of bridge.. Which, when hacked...
The best answer is probably some sort of authentication scheme between the safety critical bits on top of the basic CAN signalling, in that they won't accept commands from each other unless they are able to authenticate the sender using some sort of key exchanged when they were first paired. Then again, that makes maintenance and replacing parts more awkward.
As with everything, the cheapest route will do until customers start to notice it's woefully insecure.
