Gold Saucer could make for a fantastic venue for sure and they already showed that they can make multiple different instance when things are expected to be very crowded (showed during SHB's release). They could bring old moggle trove rewards, old event rewards that are no longer available and some new reward that could be won with MGP or a new exclusive currency to the event. That way the dev cost/time wouldn't be as high as a new area with a lot of brand new rewards. The show could be prerecorded and displayed on a board like what PSO2 does in it's lobby or something similar.