(Because I've just registered, the links referenced here need to be separately posted I think, sorry about that.)
Hello, thanks for working on such a fantastic project. It's a rather big change but what do you think of the viability of the following feature?
I'd like to be able to work with two parts of one note (like a window split in MS Word) or alternatively, look at two notes simultaneously. There have also been a few threads about very specific, custom requests regarding editor and renderer layouts , , 
The following feature (I think) is a superset to these and would offer a unified solution. It consists of a few parts:
An option to toggle the scroll coupling between panes. This is probably very easy and a stopgap solution to problems like this: 
Move the formatting tools to the top of the editor pane and unify it with these other tools:
There should be at most, one instance of this unified editor toolbar but the buttons/features available within it may be dynamic. This is probably an easy change and is only cosmetic by itself. Reasoning for this becomes apparent below.
The remainder (large lower part... the editor canvas?) of the editor pane can now be partition-able because display of a note, its title, and timestamp are decoupled from display of the formatting bar. Horizontal, and vertical split buttons can add to the partition structure. A join/merge button and a click of a partition can revert these. Clicking anywhere within a partition toggles the de/activation of the formatting tools relevant to the context of the note within that partition. This is probably a rather difficult change.
The concept of a partition or pane is agnostic to rendering method so the user can choose between plaintext and markdown for each (this is more like a feature subset of the existing layout handling). This is probably requires very little change.
My particular use-case may also be solvable by allowing multiple instances of the same journal, even if only one instance has write capability but I figure the method proposed here saves the most screen estate.
A Joplin donation bounty offer was made for a feature here a few months ago for 100 euro . In the same spirit and because my feature-set is a superset of that request, I am willing to offer an increased bounty of 300 AUD (about 185 euro) for the completion of my or any functionally compatible solution (I anticipate NorbertJh would also honour his proposed bounty as his problem would be solved as well? ). I'm happy to pay bounties for the numbered list above as follows:
- 50 AUD
- 50 AUD
- with 4. 200 AUD
I'm sorry I can't offer time to try and work on this myself right now and I hope my bounty offer isn't offensive. Joplin impresses me as the best MD journal at the moment, well done to the team! Please feel free to discuss whether this is possible and helpful or not.
Thank you for your consideration and best regards.