Due to lack of baseball, I've had a lot of time on my hands to consider where I'd like to see the MLB expand. While all of these may not be feasible, and the process of installing a new professional team is lengthy, these cities have potential.
Nashville, TN
Nashville has a somewhat central to southern location that would make travel easy for matchups with NL Central and NL East MLB teams. The city is already home to the NFL and NHL. Adding a baseball team would add more appeal to the Nashville sports scene. It is a prime tourist location already, so attendance shouldn't be a problem. Nashville has a vibe that is very similar to other MLB cities, and I think baseball could work well here.
Birmingham, AL
I struggled with whether or not to include this one, but ultimately I did. The pros of having a baseball team in Birmingham outweigh the cons. If the MLB were to expand here they would establish a large fanbase. Simply because there is a lack of professional sports in the south, aside from Atlanta. Alabama has lots of college sports, yet nothing professional. The downsides I see when it comes to expanding to Alabama is the stigma that would result. Also, the weather isn't always ideal for baseball. If any place in Alabama is worthy of a pro sports team, it's Birmingham.
Las Vegas, NV
You knew this one was coming, and it's all pros. For starters, the NHL expanded to Vegas and it worked well. The Golden Knights have been a success, and are fun to watch. Las Vegas is a clear tourist attraction, and would blend well with AL or NL West teams. The weather is always perfect for baseball. MLB needs to move to the strip ASAP.
Portland, OR
Portland is already a major sports market, but they don't have an MLB team. The city also has a major population so attendance would not be a stressor. There was once talk of a "Portland Diamond Project", that would move a baseball team into the Oregon city but efforts have somewhat faded away. If the MLB doesn't choose to expand to Portland, it would be wise to relocate there.
