This is just a pre-claim to let people have less trouble by the time Apple finally ships macOS Sierra to the public in this September / October.
As what I tested macOS Sierra (developer beta 3) runs fine using Cubase 8.5 with a fully-POWERED class-compliant USB Audio Interface (I didn’t test video-file-related functions yet since I rarely use them; If using on-board USB from your MacBook, it needs external power supply or your Cubase may quit unexpectedly).
However, Steinberg UR22 hinders my laptop from booting once plugged prior to system startup; plus, kernel panic could get triggered once you disconnect UR22 from your laptop. Thus, I urge users of Steinberg UR series to wait for Yamaha Steinberg Driver Update (with firmware updates) and install the update(s) prior to upgrade your system to macOS Sierra in this fall.
Update: Do not only update your Yamaha Steinberg USB Driver, but also: your device needs to have most-recent firmware update (for UR22 mkII, it is 1.03 at this moment). I don’t have my device with me anymore but I guess this matters. I suggest UR users to apply most recent firmware & driver updates prior to upgrading macOS to Sierra.