Before you get too addicted to importing reams of information into NotePlan notes, you might want to read up on "The Collector's Fallacy" (and further on the Zettelkasten method of learning and gaining knowledge). Here's a starting point: https://zettelkasten.de/posts/collectors-fallacy/ Note that NotePlan can be used to create a Zettelkasten, as discussed by Eduard elsewhere.
John Sobkowicz: I agree on this. I rarely copy paste something into my notes. I always rephrase something which is important for me in my own words. Though, that's not to mean this feature shouldn't be build. It definitely could be coded using the Javascript API, which supports `fetch` to load data from a website. It needs to call the Readwise APIs.
Ian I found this thread as I was looking for the same functionality. I'm just testing NotePlan out now and find it encouraging it's a possibility to do with JavaScript despite the fact I don't have the knowledge to do that. You can export your highlights as a whole or by the article/book themselves as well. The files is creates are .md which can be imported quite easily into NotePlan. If you like the default file type of .txt (which I do), you can open the Readwise created .md file in a text editor, copy the markdown, create a new note in NotePlan and paste it in. It's a bit of work but if you're like me, you like to keep your highlights intact as the writer wrote them, then do your own rephrasing or note linking within the note in NotePlan.