MLB is going to be looking hard at expansion because of the free $$$ it brings in. The group in Nashville here is pretty legit but the biggest hurdle of course is a stadium. No way they get public funding for it and finding a billionaire who will build it himself will be difficult.
Also Manfred has mentioned Nashville every time relocation/expansion comes up so I'd think we're on the shortlist. Charlotte would be very on brand for MLB (the panera bread of cities) and Portland makes sense for filling a gap in the PNW. Nashville is unique in both location (gap in the mid-south of no teams, in-between Cincy and Atlanta, driveable to Chicago, STL, etc.) and in the fact that it offers MLB a chance to partner with massive entertainment infrastructure. No other city in consideration comes close to that opportunity.
Should be pretty interesting.