I don't understand your comment about WorkflowServiceHost being limited. It is no different than a WCF ServiceHost. The WCF Service Host will host one service per host. The WF WorkflowServiceHost will host one workflow per host.
However, you can have multiple services and workflow services in you web application. In fact you don't really deal with the WorkflowServiceHost or ServiceHost classes unless you are self-hosting so they are just another part of the infrastructure most of the time.
WCF services have a collection of operations
WF services also have a collection of operations
The main difference is that the WF service can enforce a messaging protocol with certain operations being available only at certain times.
My guess is that if you can build your solution with WCF services you can also build it with workflow services.