I don't really see Messina as the Spurs head coach either. He strikes me as not a great NBA fit, in spite of his accolades. Now an NBA coach has to manage egos as much as (more than) the X's and O's, and I don't see him in that mold. Pop's the father figure of the league, and has all the big-name players' respect so what he says carries some clout. Messina wouldn't be received quite the same way, I don't think, for building this team for the future.
Would they jump over Ime and give it to Becky? I know it would piss off those in line in front of her, but I could see Pop making that sort of a statement by bringing in the league's first female head coach to replace him.