With the notion of "swinging free", Serena should win the USO this year. After that we may see a speed bump again due to reaching 24. However, that 24 is not a significant record (why this is so, is elaborated in so many other places) and so the sppedbump will be of lesser magnitude (i.e, two slams or less). Most probably Serena will do #23 at USO and #24 at Wimby'17.
The question is when will she retire? Or a more appropriate question is, why should she retire when she is at the top of the game, virtually being a contender in every slam, just because she is old as per tennis standards?