Could be that Pandora's Box is just a simple, B-movie premise a la Scary Tales over on the other coast. Like, Pandora's Box has opened and the denizens of Hell are invading the upper world! Or some artifact thieves have opened Pandora's Box!
Funnily enough, I don't think they'll use Midsummer's to give a deep dive on a completely original concept. Midsummer is an event where Murdy gets to go scene by scene on a maze, and I don't think they'll do it for an original. When you're doing a scene-by-scene of a maze based on a famous movie, there's already a hook for fans - "Here's how we do the 'Here's Johnny' scene!" "Here's how we do Dracula and his brides!" "Here's how we do the Easter bunny!" But if you have an original idea, you got no frame of reference.
And that can be exciting, true, but it can also drag on - have you ever had a friend who's a screenwriter who wants to give you a scene-by-scene of his super awesome original screenplay that's gonna be the next Avengers? And it goes on for an hour? There's nothing to keep you hooked, and you just kinda keep nodding your head. It's why people tell you to start a movie pitch with how your movie is similar to other movies, because that gives your audience a frame of reference and gets them excited about how you could jump off and twist the premise.
With that in mind, I can see Murdy using the time to announce Pandora's Box and saying the maze is a riff on famous movies like The Sentinel or Hellraiser or something, and that way the Midsummer audience knows what they're getting into, but I think it's more likely that Murdy will just take the time to announce our exclusive IP and get people excited for how they'll adapt Jordy Verill or something. I think Pandora's Box will be the last announcement, and they'll just keep it a short and sweet premise trailer: "Demons have invaded Los Angeles!" or something, and then they'll just let the audience use their imaginations.