We currently don't have interceptors, because so far they were not needed.
As for QoS parameters, this is what we use the "context" parameter for. This context is something like an IIOP service context, not to confuse with the evil CORBA IDL context
For example, both IceStorm and Glacier interpret various context parameters to determine how to forward messages, what priority to give to them, how to batch them, etc. (What we still need to do is to add the ability to set a default context, which makes programming a little bit simpler.)
Perhaps you can use contexts for the QoS parameters in your projects?