seeking advice: possible new @attribute to mark class' default property to avoid alias this ?

[rikki cattermole]

So a field that will automatically be resolved to as part of the 
behavior of generated toString methods.

That really isn't what alias this is used for commonly. I.e.

struct ValueReference {
	private {
		SomethingElse* impl;
	}

	bool isNull() { return impl is null; }

	scope ref ValueType _get() { return impl.thingy; }

	alias _get this;
}

Only the problem is, this also works for classes and whole pile of extra 
cases.