I'm seeing that there has been no activity in this thread for nearly 7 months, I'm planning to close this in the current commitfest unless someone is planning to take it forward.
This patch fixes the wrong comments in try_partial_hashjoin_path, and also simplifies and enhances the checks for parameterized partial paths. I think it's worth to be moved forward.
I've rebased the patch over current master, added a commit message describing what it does, and updated the comment a little bit in the v2 patch.