3 reputable places have shared midseason farm rankings. BA had us at 15, ESPN at 17, and Fangraphs at 19. Spencer has said he thinks the farm system is currently in the 10-15 range. BP didn't have any Brewers in their midseason Top 50 update, so I imagine they would have our farm system similarly ranked to BA, ESPN, and Fangraphs.
The farm system is young and has good depth, but depth isn't how you're going to get a high ranked farm system. Top 100 prospects are how you get there which we lack at the moment. We have a lot of players with Top 100 upside in the low minors and complex league. Pratt is a semi-universal Top 100 prospect at this point. Yophery, Bitonti, Made, Pena all have Top 100 potential. Pitchers like Meccage, Knoth, Letson have Top 100 potential although I'd say less so than the 4 position players.