Specify the sound and in kinds of @namespace:sound; pattern in speaker's string to enable it. A specific block can also make a sound along with the message such as heads (emits mob sound). Can be used on funny things like making ATOS in railway system.

There can be also minecarts with speaker, shapelessly crafted with cart and speaker, activated by activator track, and return speaker and minecart on broken.

would be quite op/ disruptive, one could scare players with arbitarty sounds, kind of like do what parrots do but way better. I thin such a feature could be a nice one but if kept for ceative use only for maps and such and there command blocks exist and can do that. Not to mention that all modes but narration wouldnt make sense when used with such sounds

Then what about the speaker cart? This can be a collab with railcraft reborn, to send message to players on the same train.