The addition of a three point line drastically changed the play-style in the NBA. It added a new dimension of scoring, and without it, we would not have the great shooters we have today in Steph Curry, Klay Thompson, and Kyle Korver. Therefore, a four point line would simply provide a new dimension of scoring. Not only would it provide a method of scoring a lot of points quickly, but it would also spread the defense and allow for scoring on cuts to the basket. 
Another question that stems from the four point line question is how far away the the line should be. A good top tier three point shooter makes about 40% his of shots, translating to 1.2 expected points per shot. To achieve that same expected points per shot, a four point shooter would only have to average 30%. Therefore, the line should be far enough away such that good shooters average around 30% from it. I would imagine that line would be about an extra four or so feet away from the existing three point line.
The next question would be whether or not to change the size of the court to adjust for the four point line, or simply leave the dimensions unchanged. I believe that logistically, it would be very difficult to adjust the court size in all 30 NBA stadiums as well as all the D-League stadiums. Furthermore, changing the size and shape of the court could perhaps change the game too much, much more than simply adding a four point line would.
Considering these facts and extrapolations, I believe that a four point line would indeed be good for the NBA. However, the NBA was slow to accept the three point line, as it was first featured in the ABL and ABA. Thus, I believe the four point line will emerge elsewhere first, and then possibly be added by the NBA if it proves to be an upgrade to the existing game of basketball, rather than a complete game changer.
The 5th Quarter 
Thats really interesting concept, but i feel like the flaws of making longer shots worth more is how far back can you go untill it starts to become less about accuracy and skill and turns into just blind luck. A good example is football, when throwing a hailmary for a td there is alot more blind luck involved then when throwing a 5yd pass for a td but they are both awarded with 6pts only. In sports luck should not be awarded more then skill. Though it is a really really interesting topic to think about, and gives a look at what people in the late 70s might have been thinking when the 3pt line was introduced.
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Good point Zach. I don’t believe the NBA could go much farther back than the four point line, as a five point line would be near half court, at which point it would rely almost exclusively on luck.
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All true, but you have to remember that players will develop the skill of shooting the 4 pointer as the game gets used to the shot. In today’s game, a 28 foot shot that goes in seems like luck because the shot was probably thrown up as the shot clock was winding down or at the end of a quarter. However, if the shot became a part of the game, players would develop their long range shooting skills, much like today’s efficient three point shooters. Not to mention, a 4 pointer would make the game more exciting as teams could come back from an 8 point deficit in two plays.
The one concern I have with a 4 point line is that it may move the NBA’s increasingly guard favored approach even more that way. Players like Curry would only need to hit half as many shots to equal the number of points, and reliance on big men may be a thing of the past. Instead of being a potential game changing force, a talented post player would simply become an afterthought.
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