I can't think of any way that a "third" TSM track would work. First, the queue is in between the current loading area and Soundstage 1. Second, while the ride path has two tracks, it only has one loading and unloading zone and dispatches two vehicles at a time. A "third" track would have to be an entirely redesigned ride system. Even if they somehow did this, having one side handle 1/3rd of the capacity and the other sides take 2/3rds would be a nightmare to for traffic flow.
Another option would be to copy and paste and mirror the entire original ride track, and I highly doubt that would happen, given that, again, the queue is in between and would have to be completely reconfigured.