1. Notes is completely open-source[1]. There are some awesome maintainers who help me fix and update things and sometimes even implement new features. When Plume will be released, of course, I'll put much less time into Notes (as already the case). But since Notes is licensed under MPL and Plume is built on top of it, all files used from Notes will be open source as well, so any improvement from Plume could be potentially incorporated into Notes.
2. The reason for creating Plume is that I always wanted[2] to create an advanced editor (a la Notion) but only recently realized how to be able to do it using C++ (handling the model) and QML (handling the view). I had to implement many things from scratch (undo/redo/copy/paste/multi-block-editing/etc).
3. I recently discussed my reasoning to go close-source[3]. I've been working night and day (every day) converting 4 cups of coffee into code for the last 4 months to create Plume. I don't want to risk not being rewarded sufficiently for it. But, I'm 99% sure that I'll either open source the core block editor or the entire app in the future.
I have a few questions for you. I apologize if some (all?) of them are too aggressive.
What were your reasons for creating a new project rather than focussing on the existing project? Technical debt?
What will be the pricing of the new app? Will it be open-source?
Lastly, will Notes be maintained by you to a lesser degree upon the release of Plume? Will you let the community take over? Will nothing change?