Personally not happy with the news, not that Brawn isn't great and wouldn't be good at the job but, for me there are two teams working well currently, Merc and RBR. The sport needs great team bosses and the sport doesn't have enough. I'd far far prefer to see a team nab him as Renault, Ferrari or Mclaren boss.
I can see him taking charge bringing any of those teams into competitiveness for 2018(too late for 2017 now), where as as the man in charge of sporting for F1, well he's not going to do much of anything before 2020 now is he. I also think he has more power to make a great team individually as a team boss than he'll have to make overall good decisions for the sport.
As team boss you do whatever you can to make your team competitive, as boss of the sport, you're in a political position where teams can vote against stuff you think will even up the sport.
So while he can certainly improve a team, he may be blocked from doing anything genuinely good for the sport as a boss.