My host (Windows 2012) was running 1 virtual machine.
I doubled clicked the iso to mount it, ran the setup, then selected install. I received no warning telling me to power off my VM.
Then selected No Thanks to downloading updates,
I then selected a GUI install
I then Accepted the terms and selected next,
I then Selected upgrade,
The install took slightly longer than 10 minutes. Once the install had finished and I logged in, the machine was on the domain, all roles and features were installed as expected, Hyper-V was fine. I powered on my Virtual DC. The DC powered on fine and there were no issues at all. This was a very painless operation with minimal downtime.