I've seen no mention of it officially from Texas A&M, but this tweet by Lance Zeirlein suggests that University of Houston co-offensive coordinator Kliff Kingsbury will join Sumlin in Aggieland in the same capacity.
Kingsbury, in case you are unfamiliar with him, was a former Texas Tech quarterback under Mike Leach who was named 2011 Offensive Coordinator of the Year for what he did with the Cougars. He's been a full-time coordinator for two seasons now and had some pretty potent offenses. He's also been a coach just since 2008 after playing in the CFL and NFL since 2004.
In other news, I feel really old now. I remember rooting against Kingsbury lustily in my college days, thinking that gimmicky Tech offense wouldn't last. Ooops. Between this and Major Applewhite being prominently involved in the University of Texas staff, I suddenly feel pretty self-conscious about what I've accomplished since graduation. (Hint: I'm not on a major college coaching staff nor covering a major college for a newspaper. Sigh.)
Will Sumlin have a bunch of input into the offense? Certainly. Will Kingsbury bring a level of experience to the quarterbacks that can help immensely in developing guys down the road? Absolutely. It's a solid hire, especially if Sumlin is comfortable working with him.
Now, about that defense...