Harrison Bader
The first player on this list is a former Cardinal and a true center fielder. Due to the latter quality, he doesn't fully fit John Mozeliak's description. Harrison Bader would be a welcome addition to the roster, but him being a true center fielder complicates things slightly.
Bader signed a 1-year, $10.5 million deal this offseason with the New York Mets, so he will be owed around $5 million for the remainder of the season after the deadline. That's not much money, but it is a decent chunk of change for an organization with a self-imposed financial ceiling.
Harrison Bader has exceeded expectations this year in Queens. He is slashing .266/.318/.367 with 3 home runs and 8 stolen bases for an OPS+ of 102. Bader has never been known as a great slugger, but there is some slight room for improvement in that area. He has accumulated 4 Outs Above Average and 2 Defensive Runs Saved this year in 57 games. He is still a plus defender in the outfield.
Bader would likely cost the team one of their mid-level prospects; New York appears to be in a full rebuild as their owner Steve Cohen acclimates to building a farm system that is rife with talented prospects. St. Louis has plenty of outfielders and pitchers in the 15-20 range of their prospect list that could be appealing to the Mets.
Bader's inclusion on the roster would make the logjam that is present when everyone is healthy even worse. He is deserving of an everyday role, and St. Louis couldn't give that to him. He's the least likely player to join the Cardinals on this list, but his history with the organization and his performance this year would be welcome this year.