I think it would be really nice if Renoise remembered the hide/show settings for each page (arranger, mixer etc) instead of globally. It would be cool if this were an option that could be chosen in the global settings, or even on a per-song basis. For example, I rarely use the top frame whilst on the mixer page, and I would ideally like it to stay off to give me more insert space. I realise that there are the global window shortcuts, but I still prefer to use the mouse for switching pages.
Does anyone else think this would be useful? Waste of time? 
I have no idea if this is a big feature change or not, so it’s just a little idea 