Trying to actually figure out what it could be, and this jumps out to me:
Keeping this in mind, there's 3 big IPs that immediately jump out to me that a) have something big coming this weekend, and b) definitely get some backlash/too good of an insane fan reaction for Legacy to get his chaos fill!
1) Fortnite - The new season begins this Thursday, and is very much leaning into being a nostalgia season with the Ice King and the Foundation. Of course, this would be possibly the most insane, out-there announcement in HHN's history, but love it or hate it, be arguably the biggest in history for GP. At the same time, however, this doesn't make much sense logistically considering Disney's ever-growing partnership with Epic and Fortnite specifically. Bringing us to the other two options...
2) JoJo's Bizarre Adventure - Arguably the most well-known and popular anime out there besides One Piece, with the long-awaited Steel Ball Run adaptation beginning this Thursday. Of the three options I propose, this would make the most sense to me, Part 1 alone could make for a fantastic house and/or zone, and since we don't have Fan Fest with One Piece, this could be a great way to introduce anime into the parks.
3) The Amazing Digital Circus - The popular indie animated series that's been a big merch-seller and even co-streams its YouTube premieres (and co-releases its episodes) on Netflix, with the penultimate episode releasing this Friday. It's a great psychological thriller inspired by I Have No Mouth and Must Scream, and from the latest teasers, it's looking like this next episode is gonna crank things up from 0-100 in the horror category real quick.