As a Requirements Engineer/Test Engineer I want to export a requirement document/test suite (segment), which consists of requirements/test cases (nodes) including their respective test cases/requirements. Requirements/Test cases are linked to test cases/requirements via a trace relationship.
It is possible to export IDs of linked items through Gateway:
Enable Gateway debugging, and it can be confirmed by looking at logfile GatewayApp.log that Gateway application is actually parsing data of linked objects. Until the following happens:
2/26/18 11:17 AM -- [Gateway-App] DEBUG(10): Flattening tree structure...
Gateway is only exporting items of one document (segment).
PTC Services has a solution to overcome this restriction (thanks to @VolkerEckardt). I appreciate this work, however, I would prefer an integrated solution for several reasons: e.g. official support, compatibility issues, etc.