Treat braces as first-class citizens
As I was working on duplicating braces from the 1960s, I realized an important limitation of both Finale and Sibelius. Both programs use a single stretched shape to handle all possible staff widths. The implications are clear: for staves that have narrower or wider spaces than the symbol was designed for, it becomes distorted and ugly. My solution? Replace the single shape with several shapes specifically designed for a range of distances. The program should dynamically swap them out as staff distances change.
Computer fonts have a similar problem. If a font is designed to look good at 12pt, it will look too thin at 6pt and too fat at 72pt. Type companies, realizing this, release versions of high-end typefaces that are appropriately-weighted. Six-point caption-weight fonts have thicker lines and are slightly wider. Seventy-two-point heading fonts have a greater difference between thick and thin lines and have more delicately-pointed serifs. Adobe has an illuminating article on this practice here. The computer won't do it for you, though. It's up to the layout designer to know about the issue and select an appropriate typeface for the job at hand. For music engravers, the choice is not quite so easy.
How did they do it before?
For much of the history of music engraving, braces were set using differently-sized punches. Each punch size would be individually crafted to have correct proportions. With the advent of photographic reproduction and dry-transfer sheets, manufacturers began to cheat. Instead of having individually-designed braces, different sizes would be taken from one master symbol and optically reduced or enlarged. Very small and very large braces continued to have their own symbols. By the time computer software started to be written, I surmise that memory limitations and programming expediency led to the one-symbol solution. Since it is generally innocuous, it has persisted to the present day.
Let's do it right.
"Generally innocuous" does not excellent engraving make. You can see in the image below what happens at large and small distances. Sibelius scales a little better than Finale, but the braces are still distorted. If one were to apply this kind of stretching to a familiar character, one can immediately see the violence done to the letterform. As the level of stretching increases, the line weights become increasingly out of proportion. With the Boosey braces, two strategies are employed. The brace at the left is the model; the middle brace is an optically-reduced version of it. The smallest brace is a unique symbol. This is the strategy I recommend to the MakeMusic and Avid.
There should be four or five unique braces, each tailored to look good for a particular range of staff distances. Each brace should be uniformly scaled to match the specific staff distance. As distances change, different symbols should be swapped in. The number of unique symbols should be enough that its extremes are not noticeable (a brace designed for a 1-space gap would look funny enlarged to fit 4 staves). This would produce the highest possible quality for these delicate and graceful symbols.