Jaime Rodriguez has just written a post about new WPF 4.0 features we can expect in the upcoming release. He mentioned a lot of new features along with some details.
Over all of those features, there are some features I've been expecting in 4.0 which has not been made into Beta 1. They are:
I also noticed it will have supports over new Windows 7's Taskbar and JumpList features. Apparently, it also supports Windows Vista and Windows 7's native dialogs which I haven't had a chance to touch yet.
I think I won't reiterate the details of the features above, instead you can read yourself in his post.
Hopefully (and desperately hoping :)) they will make it!