I don't really think it's right that Schumacher is going to fill in for Massa. I think Ferrari approched Michael because they want the press and the attention that it will generate. I can't think of any other reason to do it. And that's just taking advantage of Massa's misfortune. Schumacher has not been racing for close to 2 years, and he injured himself in a motorcycle crash earlier in the year. He isn't in the condition he needs to be in to race F1. He has almost a month to get in that condition, but will he be able to? I don't know that he will. I think Marc Gene would have been the correct replacement for Massa. I believe he's the spare driver, and he's race fit. He's also Spanish, so racing in Valencia would be something that he would really appreciate.
But I do agree that it will be very interesting to see Raikkonen and Schumacher driving in equal equipment. I would rather have seen that happen when Schumacher was still racing, because now it will not be fair to compare him to Kimi, but it will still be interesting. I wonder if Schumacher will get his former race engineer and race crew back, because they're Kimi's crew now.