Star Wars, at least as long as I've been around to observe it, has always had a ~two-tiered continuity. The first is ~G-canon, which comprises the theatrical films and their adaptations, as well as whatever George Lucas has directly influenced AND cares to include. (I.e., The Clone Wars is G-canon but the Holiday Special is not.)
The second level is ~C-canon, being most of the EU as we've known it. It's not at that higher level of canon, though it's still valid unless contradicted by something G-canon. There are some Star Wars works that do not even make it up to this level of canon that, to me, are outside of continuity altogether.
This recent announcement seems, at first blush, to say that all C-canon material is now pushed down to being outside of continuity. In reality, I think it's more of a blanket statement that they are not going to go out of their way to be consistent with past EU. In other words, what was C-canon will remain such, though it's all on probation and can be erased at a moment's notice by something G-canon (or D-canon?). In that sense, it's really not anything new.
So you can have your Darth Plagueis or Shadows Of The Empire novels, and they'll still basically be C-canon unless new material going forward contradicts it. These two examples should be relatively safe from immediate danger, whereas stuff like The Thrawn Trilogy will certainly be precluded by new content pretty quickly.
I hope I don't sound like I'm griping; this is the sort of mental exercise that is fun about a fictional universe. We're just not usually asked to engage in it with so much material all at once.
