Thanks for working on a fix here!

It could be worth checking if this fix handles the following case as well:

// This function gets included
export default (function cube ( x ) {
	// rewrite this as `square( x ) * x`
	// and see what happens!
	return x * x * x;
}, console.log('test'))

as that also seems to have the issue from my testing.

I'll let @lukastaegert do the full review for this one further.

In the example you posted I think it might be correct to remove cube as it has no side-effects and is unsed. The exported expression is the last in sequence (console.log) if I'm not mistaken.
For example swapping the two expressions around leaves them both in the bundle correctly:

// This function gets included
export default (console.log('test'), function cube ( x ) {
	// rewrite this as `square( x ) * x`
	// and see what happens!
	return x * x * x;
})

@danez ahh I see, yes you're right.

I'm wondering if it might be worth looking for a fix where the ExportDefaultVariable never passed referencesOriginal() by moving the logic into there? I believe this logic is attempting to tell when export default x is basically identical to export { x as default } so that it can be removed. So in this case it isn't, as it is itself the original (which is unique to this case).

Actually forget the above, it would be tricky to get the logic into there. This looks good to me!