Well it is hard to tell if Capriati, Clijsters, even Henin and any other top players out right now can become serious contenders again or not; or if they have dropped from the top group altogether. However among the possable contenders late in the year Capriati, Clijsters, Davenport, Henin, would all have more of a chance against Serena on a hard court than grass IMO. None of those would be favored, Davenport in top form would be closest to even odds maybe. However all would have a better chance of an upset than on grass I believe. Venus, Kuznetsova, and Sharapova's odds probably remain the same. Mauresmo's odds stay the same, and Myskina and Dementieva are much better players on hard than grass, but I dont count either of those as people that could beat Serena at the U.S open, although all could be contenders if Serena goes out maybe. So overall among the possable contenders, half would have more of a chance of an upset on hard courts, not due to Serena, but just because they arent as strong on grass as hard, while half stay about the same. That is how I see it anyway.
I have serous doubts on Capriati becoming a top contender again. I could easily see her retire before the end of the year. To beat Serena in the quarters of two slams last year, and lose in the next round each time, on the heals of her heartbreaking U.S open loss to Henin in 2003, it will be hard for her to overcome emotionaly at this point in her career. Plus she has maxed out her game I believe, I just dont think she can keep up with the younger players anymore. There are too many players who will be favored to beat her. She seems to get up for Serena but I dont think she will be enough of a top player to continue their rivalry this year.