I don't think that they will expand the league any time soon. Right now at 2 conferences, 4 divisions each with 4 teams in each league, it is balanced very well. That is 32 teams if you are counting.
Adding just 1 or 2 teams would cause an imbalance of how the games are played with more inner division games then other divisions.
So unless they add 4 teams to each conference at once, or redraw the division boundaries again, I don't see it happening any time soon.
Also, look at the NHL, they grew very quickly, and it diluted heavily the talent pool amongst all the teams. Personally, I think that led to some of hte problems that they have had in the last few years.





