I don't recall seeing a Ninth Circuit case previously in which it has granted en banc review for the sole purpose of certifying the case to a state court. But that's what the Ninth Circuit does here.
It also makes sense to me. I agree that forum-shopping and comity concerns seem to militate strongly in favor of certification here. So I wouldn't dissent from this unanimous decision of the en banc court.
Mind you, that's not what the panel did. It decided the merits. But neither Judge Reinhardt or Betty Fletcher was on the en banc draw. And while Judge Wardlaw was, she dissented on the panel, so she's pretty happy with the decision.
I think this is a good call.