Working with Mike on getting the IBMTLOG schema project working, we have come to the conclusion that Daffodil's compiler and runtime cannot correctly support trailing suppression without some major refactoring.
We can currently support separatorSuppresssionPolicy always or never, but trailing suppression requires backtracking that will need its own iterative combinators.
Pull request 55 (which should be pushed upstream soon after the creation of this ticket) includes a couple tests that demonstrate what works and doesn't work with our current implementation. I believe that we can currently support trailing suppression for required elements, but for optional separated elements things break down when the first element of a sequence is optional and missing. See org.apache.daffodil.section13.packed.TestPacked.testDelimitedIBM4690IntOptSeq02