If we look at official WTA rankings during US Open 2006
, we will notice just three (Russian) player which is still TOP10 two years later (just one player from september 2006 TOP12 is in current TOP7, Elena Dementieva, but dont forget that Elena during 2007 several months also drop from TOP10)!
1 - Amelie Mauresmo (#24)
2 - Justine Henin (N/A)
3 - Kim Clijsters (N/A)
4 - Maria Sharapova ( #9)
5 - Elena Dementieva ( #4)
6 - Nadia Petrova (#11)
7 - Svetlana Kuznetsova ( #8)
8 - Patty Schnyder (#13)
9 - Martina Hingis (N/A)
10 - Nicole Vaidisova (#41)
11 - Lindsay Davenport (#35)
12 - Anastasia Myskina (N/A)
So obviously it's hard to predict TOP10 even 2 years in future.
But 21yo Maria Sharapova and Ana Ivanovic seems like sure bets right now and not too much older Jelena, Dinara and Safina is all three over 50% chances to stay in TOP10 for sure.
Talking about sisters it's always really hard to say anything about over 30 players.
Talking about younger generation i dont see so dominant talents. Couple years ago seems that Vaidisova, Golovin and Karantantcheva will be by far best players of that "next" generation, but now seems that Radwanska, Azarenka and Wozniacki have better chances. Also dont forget some players which is in current slump but prove their possibilities like Chakvetadze, Safarova and Szavay. Of course, nobody will be surprised to see 19yo De Brito or 18yo Laura Robson in TOP10 when London Olympics starts and also never dont underrate Pavlyuchenkova chances and dont forget Kvitova.