New York Rangers at Yankee Stadium
Yes, let's run it back. The Hudson River Rivalry is the most obvious choice for an outdoor game in the national spotlight. Many had thought this should've been the matchup this past weekend. However, it was smarter to let the game be about the Devils and put the spotlight on New Jersey rather than New York and the Rangers.
The Rangers don't look like they're going away anytime soon, and the Devils should be peaking a few years from now. Having two juggernauts who happen to be massive rivals, go head-to-head at an outdoor game would do huge numbers for the league.
As for the venue, MetLife can be taken out of the running since it just hosted. Citi Field would be a good option, too, but Yankee Stadium has the size and pedigree to host another one of these games. It has a capacity of a little over 46,000, nearly 40,000 less than MetLife. However, it's much more condensed, leaving for an intimate atmosphere. There are likely a few more playoff series between these two teams over the next couple of years, further growing the rivalry, making for a perfect outdoor environment.