I love the enthusiasm!
I will play around with scaling when I find the time. But centring and changing the size of the “paper” (or cropping) is a hole other thing, that’s not that easy. In particular it’s hard if the user wants the frame+title block to be plotted (which I personally want).
Scaling has been requested by 3-4 people now. Personally I don’t see why though. I can understand why you want the pcb to be bigger on the pdf page, but why wouldn’t you want that on the page in pcbnew as well? Personally I want the pdf and the pcbnew view to be the same, and it’s easy to customize the view in pcbnew by selecting a different size under File -> Page Settings -> Paper -> Size. What downsides do you see with doing this? And I don’t mean just doing it before plotting the pdf file, but actually using a smaller page size in pcbnew when small pcb’s are designed.