It's not a bad level of soccer. I live in Cincinnati now, and we have a new USL club, FC Cincinnati, that just started playing this season to USL-record crowds. They just hosted Premier League squad Crystal Palace in a friendly that drew over 35,000, the largest professional soccer crowd in Ohio history. (Crystal Palace won 2-0.) And despite being new, FC Cincinnati is 10-3-4 and in 3rd place in the Eastern Conference. (Eastern and Western don't play in the regular season, so Cincinnati and San Antonio can't meet until the playoffs.)
FC Cincinnati and San Antonio FC both have aggressive ownership groups that are pushing hard for MLS expansion. I think your idea for a San Antonio FC forum is a worthy one.