For a big chunk of the New York city population, LaGuardia is vastly cheaper and faster to get to by car/taxi than JFK or Newark. When it's not rush hour I can be there in 20 minutes from my house. JFK is twice that. Newark is even more. While it has crummy public transport options and is a complete dump, there's something to be said for a small airport that's close to home.
One of the big downsides to LaGuardia, though, is that there's a perimeter limit on the airport – Denver is about as far as you can fly. The Wall Street Journal says that this rule might be lifted soon though.
I'm really curious what routes this could enable. People thought Virgin America was crazy when they decided to launch Newark–Los Angeles service when they already offered JFK–LAX flights, but the Newark flights quickly became profitable, so I'm wondering what the conventional wisdom here even is. Given that, I'm wondering if the fancy domestic First Class planes might do well there (United PS, JetBlue Mint) considering how business people love LaGuardia's quick access to midtown by cab.
The article mentions that it could become a destination for international flights from airports with USA pre-clearance facilities (e.g., Montreal, Dublin). Now if only they could actually build this beautiful proposed update to the place! Oh, and put in an AirTrain to Jackson Heights, NOT Willets Point and we'd be all set!