I really like the idea of having some kind of "lose shared vision" ultimate, however it would have to be losing creep and tower vision, as if it was heroes everyone could circumvent it by just sharing control of their heroes and units to everyone.I like some of the ideas here. I think NS's ulltimate should be a single target spell that causes the target to suffer reduced vision range and lose shared vision and see illusions of night stalker so he can't tell which is the real one.
http://www.reddit.com/r/DotA2/comments/2m6d8k/night_stalker_rework_suggestions/