How about a combo that when stepped on triggers the builders choice of one of the added sound slots, and maybe being able to select the sound that plays when secrets are triggered.
combo triggers sound
Sounds like a great suggestion to me. o.o Maybe we could do something like how we have four stairs / direct warps, (A through D, and Random.) we could have four "Play SFX" combos, (Five if you count the random.) where you can select the sound it'll play in the fourth page of the Screen Flags.
You can then use special combo cycling tricks (Step-->Next onto a play sfx combo, which combo cycles back to a normal, then to the same Step->Next.) to make it so that you can't dance on it and have it spam the SFX in a disorderly manner.
I was thinking more along the lines of skulltulas making their sound as you approached them, and walls making noise as they collapse, and NPC's like Gorons making a sound when you walk up to talk to them, and then being able to turn the sounds off by again removing the combo either by cycling or triggering a secret.