I have different issues with the PubSubCommunicationFlowConfigurationType and SubscriberConfigurationType.

(1) Optional on PubSubCommunicationFlowConfigurationType and SubscriberConfigurationType
Based on discussions with Paul and Georg in prototyping meetings I understand why everything is optional for the Publisher side but I do not see why the subscriber address is mandatory. SubscriberConfigurationType.Address should be optional. I assume in most cases the address can be configured on the Publisher and the address of the Subscriber is either the same or can be derived from the Publisher Address. If this must be configured by a user, it would be very annoying if a lot of subscriber addresses must be configured for a multi-cast scenario where all subscriber addresses would be identical to the publisher address.

(2) Missing configuration parameters
The following parameters are necessary if you want to support more than one protocol option in FX:

• TranportProfileUri
• HeaderLayoutUri

The message encoding is not part of the address schema. This would be a problem for the broker transports. This information is only indicated by the TranportProfileUri.

Even if the Periodic Fixed Header Layout is the default for FX, it is necessary to provide the dynamic option for some use cases e.g. autonomous Publisher.
Periodic Fixed can be defined as default if optional HeaderLayoutUri is not provided.