looks like a few female characters will be added (damn does becky creep me out if its who i think it is), and even though this article doesn't say anything about the lag fix, it was said by one of the dev's on the official prey forums that lag will be addressed by the upcoming patch (although they weren't very optimistic about how much they could improve it, so its a good thing we're getting some 2-4 player maps)http://xbox360.ign.com/articles/725/725266p1.html
According to the post, Ritual is working on the 1.1 patch which, among other things, aims to fix various bugs, adds widescreen to menus, and updates the multiplayer browser. Rhinehart also said that Venom, who developed the Xbox 360 version of Prey, is working on a patch, too.
In response to player requests for maps that function well as 1v1 maps, Ritual is working on four new maps that will work well for 2-4 players. In addition, the studio is planning six new player characters: Jen, Elhuit, Mother, Becky (a blond victim from the single player campaign), Hunter, and Elite Hunter.
The additional content is planned for the PC and X360 versions, but the ETA is no more specific than "very soon."