A lurking, distant planet is not a new idea, of course, but the last time I reported on this work ("A second Sedna! What does it mean?"), theorists were still scratching their heads over how an undiscovered planet could cause the arguments of perihelion of distant detached objects line up. The best thing about the paper, in my opinion, is that it makes very specific predictions about where the large object should be, and also about where there should be lots of other smaller worlds, providing guidance for future surveys. Brown and Batygin are looking for the object with Subaru, but the search could take five years, and if it's out there, someone else could find it first.

Since the paper was the subject of an embargo, there are lots of excellent articles out there featuring interviews of the authors as well as other observational astronomers, like Chad Trujillo and Scott Sheppard, and dynamics theorists, like Hal Levison and Alessandro Morbidelli. I couldn't possibly do better than all of these, so here's a list of good articles and who they interviewed, in no particular order:

I did read the paper, and one thing in the discussion caught my eye: the work does not explain the "Kuiper cliff," the lack of objects with orbit semimajor axes between 50 and 70 AU. It would be very nice (from an aesthetic standpoint, anyway) if the same planet could also be blamed for those apparently missing worlds. But it can't, at least not yet: