The cat is out of the bag, finally!
No date has been published yet for its release, but in the meantime you can read the first quick notes about the new features that will be included in 3.1.
I guess in the next few days/weeks we'll see more official words with details on each topic.
In this sense, Shawn has recently blogged about one of these features: automatic serialization of content binaries (XNB). So, check it out!
> Link to Spanish version.