Yesterday during The Foundry's live stream of their Siggraph booth they offered up some tech previews. Video of the presentations should be up on their Vimeo channel soon. They promised big upgrades to Nuke's paint system, including integrating paint strokes with their motion estimation tech that powers Kronos.
From what I could gather, the motion vectors that allow Kronos to interpolate frame-to-frame motion is being used to drive paint strokes. From the demonstration it looked super impressive, hopefully it will be just as impressive in actual production.
It was also mentioned that overall performance of Paint will be improved in Nuke 10. Here's hoping that's the case as I've found Nuke's Paint tool to be painful to use for as long as I've used it (and it's been given several overhauls since I started using Nuke in 2009).