Adding comments

The programmatically challenge here is that currently the scoreview is pretty much wysiwyg and exporters (for example SVG and the image capture tool) take all that information and produce their output.
It's not the notes or the anchoring themselves that pose the challenge, it's adjusting the ScoreView to have an additional "comments layer" without it affecting all other current functionality that depends on ScoreView having only the score.

I do a ton of arranging, but I do indeed use pencil and paper a lot during the process as well, not just for these sort of notes but as a basic part of the process of arranging. I also simply add staff text within MuseScore when I want to make notes to myself. I have a predefined staff text with yellow background on a custom "Annotations" palette to make it really easy to add and identify such "sticky notes". They stick out like a sore thumb so they are easy to delete later.

Thanks for pointing it to me. It's a good start.
The inconvenient with plugin-based solutions is that you can't open plugins automatically when you launch Musescore.

You bet.
I often have multiple projects going at a time, then get diverted for weeks and return. At that point, it takes some studying to figure out what it was I thought I wanted to redo or finish... or why.
A notes system with icons at selected locations would be a brilliant productivity enhancer.
In the meantime, I probably need to take screen shots and plop them into OneNote or something. ... and remember that they are there to reference.

Yeah, age hasn't really gotten to me in that respect, but productivity certainly has, that I end up doing so much that I'm like "Where was I with this?" Cause I do like about every hour or so a spin the wheel process to decide on what composer I'm going to do, which piece etc. And sometimes it can be weeks, months, even over a year before I get back to a certain score, and so yeah, having this feature would be nice. An example of how I might structure my reminder comments is:

Piece Title and catalogue number
Movement and/or section if applicable
Pages x-y of z edition on IMSLP
Instruments I still have left to transcribe
Anything else I need to do besides transcription -> Like for example, adding a playback staff for slow tempo trills.

I agree. I've been using Google Sheets to keep track of like where I am movement-wise and if I'm part of the way through or I'm finished(lots of nested IF statements in those spreadsheets) and I've been using a notes app on my tablet to keep track of how many days I spend transcribing pieces to like build up a sample average from which I can add other factors to get an upload schedule for the composer, cause I'd like to do what I did for Mozart, set myself an Upload every x days schedule for every composer I'm transcribing. And I've also been keeping track of how often a composer uses a certain key or time signature(again using Google Sheets) cause why not if I'm tracking all this other stuff.

But with a comment feature in MuseScore, I'd put in like the exact spot I'm at in the movement, what staves I have left to do in that section(cause I do a section by section approach where my stopping point before going to the next staff is dictated by repeats, final barlines, key signature changes, other structural points like that), what pages of the PDF I'm reading that it corresponds to, and any like workaround type stuff I have to do for playback purposes.