Former Orioles beat writer Buster Olney cites several sources claiming that a modest realignment could be part of the next baseball labor agreement, but I can't imagine that MLB wants to emulate the NBA playoff system by going to two 15-team leagues that would each produce five playoff teams.
The current baseball model has been so successful that MLB revenues have more than tripled since the disastrous labor war of 1994-95. Going with a system in which the top five teams would advance might increase late-season interest in some mediocre clubs, but it would remove a lot of the suspense from the regular season for the elite teams that have to battle each other for their respective division titles.
I would oppose any attempt to increase the number of playoff teams, but I could live with an extra wild card in each league, which would create a play-in series and expand the postseason to four rounds. I wouldn't be in favor of it, but it wouldn't seriously diminish the integrity of the regular season.