Hey! I'm an engineer on N1 and I can talk about (1) and (3):
1. Snoozing emails would be great. You could totally do this client-side in a plugin using our current developer APIs, by moving snoozed threads to a label/folder, and then moving them back after a prescribed time. Might be a fun project! Feel free to ping us on our community slack channel if you want to try.
3. N1 uses the exact same package structure as Atom, but we're using the CommandRegistry less, and introducing our own UI layer concepts like the ComponentRegistry (for dynamically injecting React elements.) There are probably a handful of Atom packages you could load into N1, but probably only well-contained ones with very minimal UI. Our composer unfortunately doesn't share any code with Atom's text view - we needed to do rich HTML editing, so we wrote our own composer based on `contenteditable`.
Vim keybindings for the composer are also a great idea. There's actually an API for creating `DraftStoreExtensions` (https://nylas.com/N1/docs/DraftStoreExtensions.html), and if you implement `onInput` in your extension you can probably re-create vim keyboard handling. Unfortunately, that's a bit low-level: right now, the composer is not as easy to extend as Atom's editor. We've put a lot more effort into extensibility of the thread / message panels and views.
Enjoy! Feel free to reach out on the community slack channel if you have any other questions.