A month ago Michael Rowan-Robinson discovered three dots on old images of the sky which may or may not be an undiscovered planet (that's not identical to Brown's and Batigyn's hypothetical planet). I guess it should be easy to (dis)prove its existence; when you have three dots you can easily determine the orbit and point a telescope to the location the planet should be now, or not?
Is that action already ongoing? When will we know for certain that RR's planet exists or not? May the James Webb telescope help?