While we're talking add-ons, let me throw this one out:
I'd call it "The Personnel Add-on"
Give us the ability to assign names to the muscians that play the instruments.
We all have pictures in our minds of what these musicians look like...admit it.
Each one would have a unique personality type, hair color, sexual orientation, talent level, family, etc.
We could set the salary, benefits, vacation days, etc. Of course, we can fire musicians, and recruit and hire new ones.
And have like the flute section as a real pain-in-the-[nss][nss][nss] and you have to be really nice to them and write parts special for them.
Or maybe have a Cellist that was accident-prone and was always on crutches, etc.
And a young oboist that was very interested in the conductor.
Maybe have a way to earn money to buy new instruments, new venues, etc.
Ideas are coming to me faster that I can write them down, so I'll stop.
Just my 2 cents.