Playoff baseball continues to be one of the most fun times in the sports season, so why not add more teams into the mix? When teams get off to a bad start, they tend to be resigned to losing so they can restock their farm system with better talent for next season. Expanding the playoffs will incentivize teams to build and spend money to grab those last few playoff spots instead of tanking.
It'll also allow more small-market teams to make playoff revenue and have more shots at winning a championship instead of having all of the big money teams dominate the landscape. There isn't a whole lot of downside here. MLB should change the playoff format.
One thing that separates MLB from every other league is that making the playoffs is an actual achievement. More than half of the league makes the NBA Playoffs. Baseball fans don't want their postseason cheapened and this new format will do that.
MLB teams won't be encouraged to make moves to improve the team if they know they won't have to try as hard to make the playoffs. Bottom tier teams will continue to tank and middle-tier teams still won't try as hard if they already know they're making the lower cut.
The MLB Playoffs are perfect the way it is now. The league shouldn't change it.