In a recent interview with Mindy Kaling, she reveled some details about John’s role:

Glamour: John Cho is coming on the show. I usually don’t reveal my “On a Date With…” guys until the piece runs, but he is the next column.
Mindy: I would love to go on a date with John Cho! He’s the hottest and funniest guy. When I was acting with him…I mean, I wanted to have him on the show forever! Obviously, when Selfie started, we couldn’t have him, but now we have a part for him, and he’s playing very against type. Actually, you’re the only person that knows this, but he’s playing a drug dealer.
Glamour: A drug dealer?
Mindy: Not just a drug dealer, but the head of a drug organization. Hopefully we’ll see him again, but right now he’s in one episode. [source]