Discovery Island was a "half day" experience at best, and is roughly the same size as one of the lands in the Magic Kingdom, you could maybe fit Adventureland on Discovery Island but that's about it. It was also very low tech, it had a few bathrooms on it but not a lot in terms of utilities like electricity ect...
I think the best thing they could possibly do with the Island is turn it into a mini kiddie park, a kind of half day mini 5th Gate for people with small children... you know? a place where the parents and kids could ride rides together? ...they could do things like the Fanstayland boat ride and Casey Jr train at Disneyland, the Alice hedge maze and Skull Rock area at DLP. Rides the size of the Bug's Land rides at DCA, a spinner ride, maybe a coaster the size of Barnstormer... and they could have things like meet and greets, face painting, Bibbidi Bobbidi Boutique/Pirates League ...they have room for a few small scale, low tech attractions on Discovery Island, a least a half a days worth and you could always take a boat over to the Magic Kingdom from there.
If there was some type of Theater Show or Dinner Theater Show as the main attraction, then your show ticket could be your admission to the island. They could control crowds that way by having 4 or 5 shows a day, maybe every 2 hours? so at 10am "group 1 enters", at 12pm "group 2" enters... like a cross between a Dining Reservation and the boarding passes at Rise of the Resistance... and if it was a Dinner Show, and you were required to order your meals in advance, they could prepare and deliver each group's meals every 2 hours... they couldn't really stock something like a "quick serve restaurant" on the Island and have it constantly operating... that's why Aunt Polly's on Tom Sawyer Island only ever sold Peanut Butter Sandwiches
But that would be my vote for "what to do with Discovery Island" I know our kids would have loved it when they were little, and you wouldn't need to drag a stroller to the little island, plus it could help ease the "stroller traffic" and the need for Princess meet and greets in the Magic Kingdom