It would be helpful if you could select to see the canvas in two (or more) different zoom views simultaneously.
For example when designing icons and working on a very high zoom level it is hard to judge what it would look like in 100% view or on a low resolution display.
This doesn’t solve your suggestion, but in the meantime something you could try is opening up the icon artboard in the preview window and move that window somewhere on your screen where you can always see it. Then, in the actual sketch doc you can zoom in as much as you want, but the preview window should stay at 100% zoom.
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Why did I never think of that 
Thanks, that is indeed a workaround for the time being.