Do you see Service Broker as complementary to an SDP or will Service Broker become part of SDP? How today or in next 6 years? Where do you see the best solution for 3rd party application servers in Service Broker/SDP story?

It is arguably part of a network services SDP.  If the SDP does not have a Service Broker, then it is certainly complementary.  Whether Service Broker becomes part of SDP in general is probably determined more by the future direction of SDP than Service Brokers (for example, SDP currently seems to be concentrating on OneAPI and App Stores rather than telecoms services).