I don't know...
Stirtz
Rice
Tucker
Mgbako
Maybe the foreign kid that we just got
A couple "system" bigs... Not saying he'd win a Natty, or even B10 title in year 1 with that...but nothing in his history suggests that he wouldn't be successful.
And before responding on the "fit" from any of the guys I mentioned... McCollum, from everything I've read, is a very, very process driven, detail oriented guy. So we have no idea what a guy like Mgbako might look like defensively under a coach like that...and conversely, we have no idea how impactful Tucker would be, shot selection, using his athleticism correctly, under a coach like that.
And further...there's already an established track record for quick, fairly high levels of success, with lesser heralded HS and portal kids...leading a highly successful P4 team. Iowa State has zero "blue chip" guys on their roster, Texas Tech has turned things around quickly, now multiple times, under different coaches, without obvious elite talent.
My concern wouldn't be that McCollum wouldn't come in and obviously improve our program immediately. I think he would. My concern would be more longer term, that he'd settle in to being a more "Purdue like" or "Wisconsin like" program. Solid regionally, always B10 competitive...but that maybe his program wouldn't consistently attract Final Four levels of talent.