As Seth pointed out such samples is a great model for this proposal is a good time to make that same functionality work with in-tree blocks. The QT sinks mostly accept PDUs already. What's missing is a file source that can output PDUs. Since no one is really using sigmf yet (I think?) it's hard to tell if a capture segment makes sense as a PDU since it could be some unbounded number of samples. Having a file source with fseek-like functionality controlled by async message port makes a lot of sense though. Even better if there could be some introspection to fields in the sigmf file.
I'm currently moving some more in-tree blocks to accept/output PDUs and a file source that gives such samples functions is on the list. Would be great if that comes in through a sigmf GSOC project.