Nope, 5000 is it and they're adding bushes and other sight blockers along the lake to make sure traffic flow continues around the non-seating sides during the show.
I'm on record here as saying that's stupid but I think we're misinterpreting the purpose of the theater - I thought it was going to be a single, night capping event like Wishes or Fantasmic but the number of seats is equal to the number of seats in Lights, Motors, Camera stunt show which ran several times per day. My thought is that this is planned to be a night "show" and not a night "event" (I bet the night "event" will be in Pandora)