So this is a fairly niche feature, used in higher-level code. I don't know that giving it a niche name like <one-local> x would be the end of the world.
That would certainly leave room for other ideas.
e.g. I don't think using something like $x is wise... even though it's currently available. Because I'm already thinking that might be something that says "I'm interested in the binding of this argument," and by default you don't get binding information... just to squash the spread of binding (for efficiency and potentially security)