IF MLB expands after the situations are resolved with the A's & Rays, not only are 2 sites needed for the 2 expansion teams, but also 8 other sites for the full season minor league clubs for those 2 expansion clubs.
So 2 more locations for AAA, 2 more for AA, 2 more for High A & 2 more for Low A. There is also the question of spring training / complex sites..
I suggest taking a good look at the locations that recently lost minor league teams. While a number of those locations lost clubs for good reason, I am sure a few of those cities will start pulling out all the stops in order to regain a full season minor team..