Does Mathematica 11 work on MacOS Sierra?

Yes, it works well. No issues, other than crashes when opening fonts, yet.

EDIT 2016-10-06: I just tried version 11.0.1.0 and Graphichs3D is working!

Not working at all with Graphics3D. Evaluating the following line and trying to rotate the graph with the mouse completely freezes my mac.

Graphics3D[Line@{{1, 2, 3}, {2, 3, 4}, {4, 5, 6}, {5, 6, 7}}]

The only way to fix after that is to hard reboot my laptop. @user5601 Can you try the above code and reports on the results? I think your system is similar to mine.

Yes, Mathematica 11 works fine on macOS Sierra 10.12. Currently, I am running it on the following platform:

Mac Mini (Mid 2011) 2.5 GHz Intel Core i5 8 GB RAM macOS Sierra 10.12

All the best, Richard