There was a time when Kings Island had four indoor ride through attractions operating at once. Flight of Fear, Tomb Raider or The Crypt, Action Theater, and the kids dark ride all brought something different to the park, and together they created a level of variety that made the indoor lineup feel complete. When you compare that to today, where Flight of Fear and Phantom Theater are the only true indoor rides, it is easy to see how much that part of the park has shrunk. A third indoor attraction would not be unusual for Kings Island. It would simply move the park closer to the variety it once offered.
Phantom Theater is a great addition, especially for families, but it cannot represent every type of indoor experience on its own. Kings Island used to offer several different styles of indoor attractions at the same time, and there is still plenty of room for something with a different style or tone. An interactive ride, a more modern concept, or a lighter themed attraction would fill a space that the current lineup does not fully cover, and it would give guests another option that fits outside the coaster focused offerings.
This is where Action Theater naturally comes up. The original ride is gone and the inside is now used for a haunt, but the type of attraction that once operated there filled a role the park no longer has. Kings Island already has many haunted houses, so using that space only for seasonal events does not bring much to the main season. If the park ever found a way to bring back Action Theater in some form, or create a new indoor attraction with a similar purpose, it would reintroduce a style of experience that is currently missing.
Adding another indoor ride would not repeat the past. It would simply expand the lineup in a way that feels natural for Kings Island. A new attraction inspired by the spirit of Action Theater, or a completely new concept altogether, would round out the park in a meaningful way and bring back a type of variety that used to be one of its strengths.