Agree that IF the interference was INTENTIONAL.. then definitely a DP.
Agree a retired runner is treated as a live runner in this case.
However 8-4-2-g covers all interferences.
I just don't see how R1 returning can not be interference.
8-4-1-h
SECTION 4 RUNNER IS OUT ART. 1 . . . The batter-runner is out when:
h. any runner or retired runner interferes (2-21-1, 2-30-3) in a way which obviously hinders an obvious double play;
Also in 8-4-2-g
g. intentionally interferes with a throw or a thrown ball; or he hinders a fielder on his initial attempt to field a batted ball. A fielder is not protected, except from intentional contact if he misplays the ball and has to move from his original location; or his being put out is prevented by an illegal act by anyone connected with the team (2-21-1, 3-2-2, 3) or by the batter-runner; for runner returning to base (8-2-6); and for runner being hit by a batted ball (8-4-2k). If, in the judgment of the umpire, a runner including the batterrunner interferes in any way and prevents a double play anywhere, two shall be declared out (the runner who interfered and the other runner involved). If a retired runner interferes, and in the judgment of the umpire, another runner could have been put out, the umpire shall declare that runner out. If the umpire is uncertain who would have been played on, the runner closest to home shall be called out;