The stadium cycle has pretty much run through MLB. There are your last old gems in Fenway and Wrigley, a couple expansion era gems in Dodger and Kauffman. Meh stadiums in Anaheim and Oakland, and ugly domes in Toronto and Tampa. The rest are The followers of the Camden Yards retro model, except one: Chicago White Sox appropriately named Guaranteed Rate Field.
The Braves dumped Turner, which is now the stadium for Georgia Tech.
Texas is building Globe Life Field to replace Globe Life Park, which, as new as it still seems to me is actually the 11th oldest park in MLB.
I doubt the White Sox get a new stadium anytime soon, so I'd vote Texas, seeing as the balls are rolling.
Still seeing that the Raiders are gone, and real-estate in Oakland has gone through the roof, I could see something happening in the East Bay pretty soon.
TB gets honorable mention.
I guess my real thought was by 2050, how many of these current parks will still be around.