Sorry, I have to disagree. Specific Nicktoons, really just Spongebob, may be relatively evergreen IP, but the larger Nicktoons brand and lineup are intensely 90s, and very much marketed and sold within the context of the 20-30 year nostalgia cycle.
TV ages culturally a lot faster than movies, theatre, or video games. There are only a few tv shows that I would consider truly "evergreen" and not outdated by today's standards. Even cultural juggernauts like The Simpsons are reaching the end of their effective lifespan. Kid shows age even faster, and a number of the most evergreen series' within that space also have larger brands they are attached to such as Transformers, Pokemon, Power Rangers, TMNT, My Little Pony, etc.
IMO Nicktoons aren't marketed to kids anymore, they're aimed towards young adults. I don't think we'll see much more Nicktoons within theme parks, for very similar reasons to why we didn't get The Goofy Movie taking over RnRC. If they wanted to hit that iron while it was hot, they should've started building 4-5 years ago. At this point, even the nostalgia cycle with millenials and Gen Z will be largely over by the time anything opens
This is all within the conversation of theme park expansions, which take a long time to build, cost a lot of money, and need to last for potentially decades. The characters and shows might still be watched and will probably continue to get T-Shirts and funko pops for a long time, but for theme park attractions and expansions? I believe their moment is pretty much done.