But they haven't created a "potential RBI" stat, that would be absurd. Just like a potential assist stat.
Yes they have.
Expected RBI Totals: The Top 267 xRBI Totals for 2013 | Community – FanGraphs Baseball
It's not completely analogous to assists, but the idea is the same. The goal is to remove as much "noise", or things out of the player's control, from the process.