I feel like if the third park has Lord of the Rings, Zelda/Pokemon, DreamWorks, Star Trek, Fantastic Beasts, and whatever else they can fit in on the side, it'll have enough appeal to attract people.
I think when building a new park, IP won't be the only thing that matters. When IOA opened, it had MSHI, Toon Lagoon, Jurassic Park, Lost Continent, and Seuss Landing... the only one of those that was super huge and relevant at the time was Jurassic Park. Otherwise, Toon Lagoon was dated then and is dated now, Lost Continent wasn't based on an IP, MSHI was built when Marvel was not doing great, and Seuss Landing was based off a timeless property but was also the park's "kid" area and not a huge draw. Yet despite that IOA managed to do... relatively well. I say "relatively" because there were some things that put a hamper on its success, like "Universal Studios Escape" and shortly after that, the 9/11 tourism crash. But those factors weren't the park's fault, and besides those, IOA was a fine and well-rated park. Not all of the IPs may have been the most relevant, but the park had great and (at the time) unique theming as well several amazing world-class attractions.
So with this new park, not every IP needs to be a killer WWoHP/SW:GE/SNW-level thing. Lord of the Rings would deliver on that, definitely. Pokemon would deliver on that as well, if they choose to put it in Park 3 instead of IOA. Then DreamWorks, Star Trek, Fantastic Beasts, and Zelda (if they choose to go with that instead of Pokemon) could deliver on being supplementary to those huge IPs. As long as the park is extremely well-themed (if they're truly aiming to be like TDS, it will be) with amazing, state of the art attractions (this is Universal we're talking about, of course there will be), and a bit more of a family appeal than the other parks (DreamWorks and Nintendo are already basically shoo-ins), than I think it will have plenty of appeal and draw.