I've always thought Busquets is overrated, and I could see Song get a lot of playing time.
Wish Song good luck with that. Yaya failed when Busquets was 21 and had played in the 3th division a year before. Now with the experience of winning 2 CLs, 3 La Ligas, 1 WC and 1 EC, it might be a bit harder to lay claim to his spot.
As pete correctly pointed out however: Keita was our most capped player in 2010 / 2011. Song will get Keita's time. And even more since he's even more versatile than Keita apparantely. It's a squad game after all. Busquets can't play 70+ games in a season (including national team duties) and Mascherano is a CB permanently now. I also have a feeling that Song will play alongside rather than instead of Busquets in most games and Iniesta will get shifted to the left "inside forward" spot quite often to continue his awesome relationship with Alba.
Someone who brings a bit steel into the midfield area without being completely limited like Tiote or De Jong is what Tito wants. I don't think Song will play in the back 4. Pique, Puyol (who wants to do a Maldini and play until 40+) and Mascherano are proven in that position and Bartra looks amazingly promising. If you look at Real Madrid, they don't have more options there. Ramos, Pepe, Albiol and 1 talent: Varane.
Feel sorry for Arsenal though. Barca must have contributed with € 100 million in Arsenal's new stadium by now. I'll be genuinly rooting for them in the Prem this season (also because of Cazorla's awesomeness ). I hope this helps a bit. So let's start: feck YOU FROGGY FOR RIPPING US OFF OUR CAPTAIN! PIG HEADS WILL BE THROWN AT YOU IN THE EMIRATES!*
*Hm. Nah, doesn't really feel like the Figo saga.