I wonder how parties would develop if PR became a state. I doubt they'd be willing to shed the NPP and PDP so quickly in favor of the mainland parties... maybe we'd see regional party reps elected who'd caucus with the main parties in Congress?
They would be shredded fairly quickly. Most politicians in Puerto Rico declare a loyalty to mainland parties as well as their local ones. Regionalist political parties would not go down well and would be excluded in Washington.
They could just go the route of the Minnesota Farmer Labor Party.