I use the Stop After Current command regularly, and it would be helpful if there were some visual feedback, so that I could tell at a glance whether SAC is toggled without going into the menu.
I've noticed that when I activate Auto-Shutdown, a message now appears in the status bar, e.g. "MusicBee will close at the end of the playlist." I'd love the same thing for SAC. It solves the issue and doesn't require any new UI elements.