TL;DR: Basically, my idea is a sort of OneNote for scores; a way of keeping ideas in one place, but remaining distinct.
I recently was struck by the fact that it is simply a lot easier to jot down musical fragments on paper, even if Musescore and a MIDI keyboard is handy. One disincentive to using Musescore is that making a distinct musical 'idea' really requires a separate file to keep it distinct from other semi-developed ideas, even if it is only a couple of bars long. This could of course be remedied by having one 'note-taking document', and separating each fragment by some bars, but that implies continuity where there is none. That also does not solve the problem of fragments for different instrument combinations. For example, I would rather keep a piano fragment and an SATB choir fragment separate, and not try to place them on the same stave arrangement.
A potential solution for this problem would be to have a special kind of Musescore document, structured differently to ordinary scores. Instead of a single contiguous musical line, multiple "sketches"/"fragments" could reside within the one document, each with their own instruments, tempo, title, etc. They might be in tabs, or pages, etc. (perhaps down the right side of the window?)
I acknowledge this would be no small effort to implement, and would take a lot of work, and I would be happy to contribute. However, I am interested to see whether others would consider this useful or not.
A very useful idea.
It could also be useful for storing recurring themes or motifs.
I think something like this could be valuable, although I suspect everything would have a slightly different notion of what it should entail. One thing I see as being valuable about this type of idea is using it as a "scratch pad" for unfinished ideas, which starts to resemble the common request for a new note entry mode that allows you to enter pitches with no particular rhythms, then add the rhythms later. In my case, I do this sort of thing on paper pretty often. First I write in note heads only, then draw in bar lines, then later work out specific rhythms.
I think I'd find an idea like yours useful if it had this sort of note entry mode, but I doubt I'd find much use for it if not.
In reply to I think something like this by Marc Sabatella
I agree, that kind of "scratch" note-entry mode would be very useful and make the feature work far better.