[Layers > Artboards > Focus]

I agree @Petar Petrenko, this would be really nice when working on a bunch of different versions. Also would be there was a companion "Zoom to Fit" for the focused area.

[Equivalent of Illustrator's "Add Anchor Points" Tool]

+1. I found it really confusing when I couldn't add extra points to a shape with  the pen tool, and constantly retracing the shape so that I can add the extra anchor seems inefficient, to say the least.