These could both give you a big castle and a spooky dark ride, but they are at total opposite ends of the IP spectrum for both child friendly, and current marketability. Remember the Tom Cruise Mummy was supposed to kickstart the whole Universal Monsters Universe. It did not.
HTTYD is popular, but not gangbusters popular. But I guess they could just clone a ride from Beijing that way.
I don't see the Monsters lending themselves to rides that well. Old movies simply didn't have much go on in them. Sure, you could storm Frankenstein's Castle, go through the Swamp. Enter Drac's castle. I guess an "All Monsters" dark ride would work, just like they are doing with HHN this year. But then, besides a really cool dining possibility (much more than Monster's Cafe), that would be it. I mean, a Frankenstein inside coaster and Dracula's castle dark ride would be cool, but would they be FANTASTIC in 2023?