According to Macrumors, there is a compatibility issue which means Nvidia might be out of the picture for a while. Nvidia is only capable of driving dual 5K displays with the Polaris GPUs with DisplayPort 1.3 which is not supported with Thunderbolt 3.
http://www.macrumors.com/2016/11/14/late-2016-mbp-amd-gpus-s...