Davenport, Hingis, Serena/Venus will still be around, but the only question would be whether they will still have a desire to win. I could see Lindsay still wanting to be the best in a few years, same for Hingis. Serena will prabably be too wrapped up in all her acting and other outside activities she wants to get involved in. I have always thought Venus treated tennis as a job, I don't think she really has a passion for it, so maybe in a few years she will think she has had enough of it and leave. The only 2 top players still around all the time will most likely be Hingis/Davenport.
That leaves a lot of spaces open for plenty of young players. I still see Hantuchova, Dokic, Clijsters, and Henin being around. As for the Russians, there will be many of them in the top 50. I personally see it as being a toss up over who will be the #1 on any given week. Dementieva, Kournikova, Myskina, Bovina, and Zvonareva are the ones that I see being in contention, and that is just because I haven't had the chance to see a lot of the younger ones play, so I can't put them ahead of those 5.
"Age Is Overrated"- Martina Navratilova