Pen and paper let you move ideas from your mind to a notebook fluidly.
Computerized copy and paste lets you quickly remix and combine materials from different sources, but is restricted to the digital domain.
Currently, if you want to incorporate other materials into your physical notebook, you either have to recreate them with your pen (possibly tedious and error-prone), reference it (which requires you to look it up again later), or print/photocopy and paste it in manually with scissors and glue, which imposes a high-effort barrier to rapid, fluid ideation.
An ideal copy-and-paste solution would let you effortlessly incorporate external physical and digital materials, diagrams, and sketches into your physical notebook, so you can both augment and expand upon your own physically-penned ideas, and interactively annotate these newly incorporated materials.
A demonstration of this concept: