Yesterday, Microsoft made the first Community Technology Preview of TFS 2015 available. This is not a supported release, so don't upgrade your TFS 2013 instances (or if you do, please don't call me when things break! :))
This release has a lot of the good features that they've been adding to Visual Studio Online for the past few months, and also has an early version of the new build system I was raving about earlier this month.
You can get all the juicy details and find download links on Brian Harry's blog.
Sadly, no news on the Release Management front yet. Hopefully we'll see some updates there in the near future!