You cannot yet install AADSync via AADConnect using a Windows 2016 Technical Preview 2 with a 2016 Forest.
I installed a DC on Windows 2016 with 2016 Forest.
Then I went to install AADSync, and got this error indicating that the 2016 Forest is not yet supported by AADSync.
I imagine that companies wont be in a great hurry to upgrade their Forest immediately anyway when 2016 goes GA, but I have reached out to Alex Simons for an update on when this will be supported. I will update this post if I receive a time line for this.