Message based WCF service

It all depends on the set of tasks to be performed by the service. I would say, for a fixed set, it's always possible, but usually makes no practical sense. Actually, it's not quite clear what do you mean by "one generic request" and response, but it may mean that you want to have only one method in your service contract. Why not? But again, I cannot see how this limitation could be helpful.
It would be pretty much as saying: "I want to write a library assembly which exposes exactly one method to the referencing user's assembly". If you want it, do it, only why?
—SA