I just got off the phone with DeAnthony Arnett's brother, Ralph, who helps DeAnthony with his recruitment. They have a solid group of schools that make up his top six, and there will only be one school that could be added.
The top six is (in no order), USC, Cal, Oklahoma, MSU, Tennessee, and Iowa. The wildcard that could be thrown in, if they offer, is Miami.
Apparently, the recent quarterback commit to Miami, Teddy Bridgewater, really likes DeAnthony, and wants him at Miami. The only reason Miami hasn't offered yet is because their recruiting coordinator left, and coach Shannon never got to finish watching his film. It seems like they might be a big player, if the offer comes.
Ralph told me his take on everything with Michigan and DeAnthony is that at the end of the day, he has to do what's best for him, and he doesn't feel that offense will get him to the next level. He dropped Notre Dame for the same reasons, and said the only spread he would want to play in is Oklahoma's. It has nothing to do with the coaches at Michigan, who they think very highly of, or any other reason. Both Ralph and DeAnthony think that Rich Rod will have a lot of success at Michigan, it's just not the place for him to be a big time receiver, like he wants to be.