In the Select Instrument dialog, add an option to playback a single note of each instrument when it's clicked on
I tend to choose my instruments by timbre much more than by name, as I work mostly with electronic music and use Musescore as a rough draft or clarification of something I'm going to put into a DAW. I often have no idea what MIDI instrument would be closest to the sound I'm using in the DAW, so I have to spend a while trying out different instruments to see which one approximates it the best.
If there was an option, either in preferences (or better yet, in the select instruments dialog itself) to play a note from each instrument when it was clicked on, it would make things a lot easier. I wouldn't have to keep opening and closing it over and over to see what each instrument sounded like.
Oh also, if does end up being added and the option is within the dialog vs. being a preference in the options, it should stay ticked/unticked if you close and reopen the box. I imagine most people would have one setting they preferred, and wouldn't want to have to change it every time.