I really like the original ending as well because as bittersweet as it is I'm about as confident(IE not at all) as Shiki is that he could handle not going after her. It's very bittersweet but hopeful.
I'm hoping they don't just tack something on but rather completely change the route so that we can get something entirely new that stands on it's own without stepping on the original route's essence. That way they can set up a different future maybe leading to more Tsuki content. I'm totally expecting some meta "You've already experienced this, boy, here is your evangelion and your eclipse, good luck this go around".