Hi Paul,
That's an interesting analysis. One thing I think might influence the choice is the naming of the notes in the scales when someone learns a transposing instrument. I did a year of Bb clarinet at school, but half a century later I can't remember how it was taught in this aspect of note names (in fact, I'm not 100% sure it was in Bb, but let's say that for argument's sake). In other words, did we call the Bb "C" (as written) when discussing the music, or Bb, as sounded?
The reason it might have a bearing on the question is because, although the notation may be just as easy to read in any key, some of the thinking and talking about notes still relies on the unequal naming system, either with sharp and flat names for the 'black notes' or new names, as per Express Stave and others. I'm not sure how important any of that is.
Another thing is that the increasing use of digital devices to write, typeset and read music from means this issue is perhaps less critical than it used to be with manuscripts. Most music apps allow transposing of whole pieces or sections to any other position on the staff, so each musician could choose their preferred key to read from. I guess some apps will only do transposition with the implication that the pitch is changing too, but presumably the better ones allow for transposing notation without changing pitch (precisely for transposing instruments), and it isn't particularly significant, perhaps just causing issues if you want to use the app to play the notes so you can practise with that help, which would be disturbing in another key.
I'm grateful for your thoughts, because I was beginning to wonder about this aspect of notation when I was last working on my own system, and, after a long break, I'm hoping to pick up where I left off. I remember saying it was a few weeks from being finished. LOL, I'm now hoping it might be some time before 2024.
All the best,
John F