main view should exactly mirror speaker view
The speaker view is very useful. To allow the presenter to face the audience the whole time, all interactions with the presentation should be doable on the speaker view and be mirrored on the main view. This works for drawing and annotating, but not for zooming manually. If possible, the viewport on the main view should follow the speaker view and vice versa.
I'm using Firefox on MacOS
Yes, I will make the manual zooming be synchronized between the two presentations, but there will always be some non-synced things: eg you start a video by clicking on it, ..., and every "non-slipshow managed" things.
So I'm considering another approach: add a simple way to mirror the other screen you're presenting, while still seeing the notes. It's also nice if your presentation features a demo where you're showing an editor or something like that.