Well some basic sound handling like having entry and exit points on a sound node allowing a sound to be sync with another without a strong cut in and out. To make this it would be more effective to have a dedicated window pretty much like the animation tracks with basics sound editing functions.

More sound node type, like a node with multiples sounds/audiostream inside that can switch from one to another depending on a var state. A node that plays audiostream in sequence or at random.

Just check the basic functions in Wwise. Godot is powerful enough to skip entirely the use for a audio middleware for adaptative music...