Questions moving to 2017

They didn’t change it. Evidently you turned off the warning. The default state is for that warning to be active.Turn it on again in Preferences>General.

It’s still locking. It shows you what its using as the reference for the lock.

That’s been a separate plugin for many years. Nothing new there. Pro-only.

The graphics for the toolbars are a branding thing. They were changed after Trimble bought SketchUp years back. Changing appearance for branding is not unique to SketchUp.