Maybe plan-pnode should merge into plan-core since basically pnode is lockstep with the plan data model (aka plan-core). Since pnode sits between the pdi and and client, pnode is 1:1 and tightly integrated with plan-core.
The con that I see is that plan-core would have a small set of files (formerly this repo) dedicated to building pnode. These files could live in a subdir "pnode" and I'd be ok with that.