Yes, when I said that about a probe mission, I had only heard one rumor. I think it was on Wikipedia, so it obviously wasn't 100% reliable.
So, it seems like it is pretty hard to get a probe to this planet. If it is really as far as NASA says it is, that would be quite a feat of interplanetary rendezvous to get the probe in optimum position.
Rising Fury mentioned that it is possible this planet may not even exist in the first place, which is an important point. I found the research PDF for the full physics of the matter at this URL:
http://iopscience.iop.org/article/10.3847/0004-6256/151/2/22/pdf. Maybe this planet does not exist, but the abstract of this paper states that "in this work we show that the orbits of distant Kuiper Belt objects (KBOs) cluster not only in argument of perihelion, but also in physical space. We demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance, thus requiring a dynamical origin." Even if this is not a planet, or maybe it is more than one object, there just might be
something out there causing this occurance. That's what makes the topic so interesting and mysterious.
So, we don't really know where exactly it is, or what exactly it is. I say that if we can get a relatively small margin of it's location, not perfectly accurate at all necessarily, that one could still send a probe. What about sending a telescope on this probe? It could search the entire area for this planet using this telescope, and even if it was off by an AU, it should be able to at least see the planet, right?
In short, if one were ever to send a probe to Planet 9, tremendous dV would need to be reached, there would not be a perfect envelope of accuracy, and the probe would need enhanced zoom-view capabilities. It's time for NASA to do the impossible . . . again.
Thanks