I know this is controversial, but the last 4-5 weeks of the regular season I saw alot of teams winning the coin toss, and electing to receive. Yes this is the SB, and OT but these are supposed to be professionals. Nothing wrong with giving the D extra rest.
Sooner or later you have to score on offense to keep up. I see nothing wrong with the decision. If they score a TD, and Shanahan goes for 2 and gets it, then he's a genius.