It's a step in the right direction. Sure there will probably be a long while before we even see a gay couple in kids shows even kiss. All Korra and Asami did was holding hands romantically (which some people didn't even get) and that was considered ballsy.
So we're still at a point where just suggesting a lead character in this case is gay is the most progressive thing to have ever happened in the history of children programing, hell maybe in the TV show history whereas in the more adult shows it's not uncommon for it to have gay characters but they are mostly the gag-character or a best friend, and if they are the lead of their own show it probably in a show which uses their sexuality as the main premise of the show (Will and Grace, L Word etc).
But anyway I was glad that Korra and Asami hooked up, it was the best possible outcome when it came to possible romantic relationships since her relationship with Mako was very stale and awfully forced (understandable since it was actually only meant to be 1 season) and didn't feel genuine, while her relationship with Asami didn't come out the blue for people that had noticed the subtle in season 3 and 4.
Or maybe I just want my Korrasami fanfics to be legit. WHICH THEY ARE!