For a number of reasons, I think Paul was the "rich guy" in Mark 10:17 - 31, the guy who comes up to Jesus and says "hey did all the commandments of the law ... where is my reward?" (lose paraphrase). I think that when this accepted as a distinct possibility (I am not the first person to see a connection here) everything starts to make sense in early Christianity. But for the moment, as I have not laid out my argument for identifying Paul as the "rich guy" in this pericope, I will say, what has been overlooked in the study of Marcion is the necessity that Paul "must have been" in the gospel of Marcion. I think if people look into Tertullian's account of this pericope (referenced as being in Luke of course) and notice a parallel exists between (a) Tertullian's textual critical approach with the Marcionite gospel generally (b) certain "textual critical" features in Tertullian's account of this pericope in particular (assumed to be in Marcion's falsification of "Luke" again rather than - as with the Philosophumena's Marcionite expansion of Mark) and (c) Clement of Alexandria's discussion of this pericope in the Alexandrian text of Mark it all comes together.
The Alexandrian tradition venerated Paul as if he was in the gospel (the gospel of Mark).