I think the idea of implementing a set of custom pens for each notebook or page would be very useful.

I often jump between different notebooks and each book might have different pen colours and sizes. However, as the pen presets are global, I have to continually change pen attributes.

So, for example, I might be brainstorming with an A1 page or the infinitely canvas when it’s rolled out ;-) and an A4 page. Although there are three user presets they are the same for all notebooks (global) and I still need to constantly change them (size & colour).

If the presets applied to each page then I wouldn’t need to spend time changing my pen each time.