I know this might be a little premature, but considering that the Habs and Rangers want to play outside next year, add to that the closing of Yankee Stadium. I think we may see something like this happening next year.
They said it probably wouldn't be the Isles or Devils.
I guess maybe the Capitals or the Blackhawks
the goal of the event is to attract a large TV audience. Having two NY area teams would turn it into a metro NY event. They aren't worried about selling out, which will happen regardless of the teams so they'll probably look further away for another team.
I think the Blackhawks are about 2-3 years away from being involved in an outdoor game. Bettman would probably want to wait until their a competitive team (i.e. when Toews and Kane develop) and has said that an outdoor game at Wrigley is a possibility.
I would guess the league wants to expose Ovechkin like they did Crosby this year. Having the star power is crucial, so i could see Washington. The other possibility in my mind would be Detroit, as it would be nice to get a Western Conference team in there, though i think a Minnesota/Detroit game would be amazing and should happen in 2 years.
Since it seems like the NHL wants to make it a yearly thing, its fun to imagine the schedule for the next couple of years:
Rangers/Caps at Yankee Stadium
Red Wings/Wild at (Either or)
Blackhawks/Leafs at Wrigley
Bruins/Habs at Foxboro
Kings/Sharks/Ducks/Coyotes in Vegas (they need another Vegas game)