While the PTR isn't up and active yet, we're very likely to see it within the next couple of days given the information that Ghostcrawler has been handing out lately, or even later today. The full patch notes have seemingly already leaked, so we have them for you here as well. It seems that we're getting patch 3.0.8, not 3.0.4 like we've all been saying. Not a big deal in the end, but interesting nonetheless.
Reading through these notes, keep in mind that they're probably not complete and we'll see updates to them when the PTR itself goes live. The test realm always has quite a few undocumented changes as well to keep an eye out for. Again, when we know more, we'll let you know.
Edit: Updated to reflect the official patch notes.