Getting playing time for Craig in MLB is going to be pretty difficult I think, barring an injury. It basically would require a position switch and also trading Polanco, the latter of which I can't imagine happening until the offseason.
With his great season and now selection to be in the MLB futures game, I think it's a good idea to think about moving him. You can also sell high on prospects. I don't know that I'd do it straight up for a rental, but if the team continues to win, it could be the nucleus for a competitive package for Stroman or Boyd. Boyd would be an especially interesting guy to target with a Keller + Craig starting point, because his years of control are really good. Detroit's system is in shambles, so solid quantity will probably be almost as important as solid quality at the top of the deal. Maybe Keller, Craig, Alemais, and somebody like Juan Pie or Cal Mitchell as a really nice fourth piece would be enticing enough?
I dunno, again, I'm not fully advocating something that huge, but 1) it is possible to try and develop solid depth for yourself and take advantage of it in multiple ways, including a big trade at the right time (and just because the Archer trade was ill advised and then potentially has backfired enormously with Glasnow's development doesn't mean it's always a bad idea), and 2) setting aside all of this stuff, Craig has nowhere to play, and converting him to a bad defensive RF to break him in is a full-blown rebuilding move IMO. He's perfect trade bait for this summer if we're in a good position.