Would it be possible to add a tracking button, for instance in Text preview window? While doing kerning I would find it very handy to see my typeface with different tracking (tighter or looser). What do you think?
That is on my list.

Any update on this feature?
It’s planned, but I cannot give you a timeframe just yet.
Just want to add my +1 hoping that this can be part of some future build. There’s absolutely no pressure, but if it were to be rolled out at some point, I would find it super helpful.
Also want to say that I find working in Glyphs to be so deeply enjoyable. Amazing product, and great community. Thank you so much for creating it.
We are working on tracking and other common layout options for the text preview. It will still need a bit of time but we are getting closer.
This is great news, but please don’t feel any pressure. Glyphs is already awesome!