They just did for Cliff Lee.
CC will be 31 when the 2011 season ends. Most likely, he'll be coming off another top 5 in the Cy Young award voting kind of season. The Yankees desperately wanted Cliff Lee and the thought of losing Sabathia will be intolerable. Imagine the leverage if Pettitte doesn't return, AJ continues his decline, and Hughes has a bit of a disappointing year. If that happens, Sabathia will be worth, to the Yankees, well in excess of $25 million a year.
So I don't know if he'd opt out, because maybe during that window they work out something, but I expect CC, in some shape, matter, or form, to sign something with NY that keeps him there through 2017 at least, with those last 2 seasons being worth between $25-30 million per season (whatever pulls his AAV from 2012-2017 above $25 million per).
He's in the catbird seat, really. If he has a crappy year (unlikely, but possible), oh bummer, he just sticks with his current $23 mil per year contract. If those things I describe above happen, there's no doubt he's going to sign a new deal or an big-time extension.