With Elena Kagan, we will have 3 women on the Supreme Court. 3 out of 9. It will need to go all the way to 5 in order to mirror the population (which is slightly more than half women). Some people might think women are well-represented if there are only 2 or 3 and that there is no need to reach population-proportion or that Supreme Court appointments shouldn't have to do with representing various groups. But that not what my prediction is about.
I think Presidents will continue to appoint women to the Supreme Court because they will want to make a show of appointing women to high positions, but they don't particularly want to depend closely on women in their immediate sphere of action. A Supreme Court appointment is extraordinarily high-profile, but once the appointment is made, the individual is off in separate sphere, disconnected from the important work of the presidency.
Of course, a Supreme Court opinion may have a big effect on a President's power — Truman's seizure of the steel mills, Clinton's line item veto, Nixon's audiotapes, etc. etc. But that's all the more reason why a President should want to stock the Court with highly competent women who have worked relatively closely with him. Not only does he deflect attention from the way he's kept women out of his closest inner circle, he gets a Court that understands and sympathizes with presidential power.
There are also huge numbers of women going to law school these days and acquiring brilliant credentials. A President who wants to look as though he respects and values women can easily find many women to appoint to the federal courts and there will always be great candidates for elevation to the Supreme Court. I'm seeing a dynamic that will concentrate women in the judiciary. I'm not saying this is good feminism. I intend this post as feminist critique.