I've looked through all the suggestions that have been made and worked them into these ideas:
Sports (Not only Yooyuball, but doesn't exclude it. There's also suggestion of a sub-theme about "Refereegate" for Yooyuball where an incident has caused major rules change (leaving both the incident and rule change up for interpretation)).
Ghosts & Monsters (Neopia has many beings which aren't your plain ol' Neopet, Faerie, Petpet, or Petpetpet)
Traveling Adventure (Neopia is filled with action, excitement, & mystery with lands covering wide genres)
Caves & Catacombs (With so much above the surface, many forget the surface's area doesn't even make up 1% of the planet's mass. That means there's a lot underneath, and both natural and manmade forces have taken advantage of that)
In the Sky (Same as with the ground beneath, the sky above has shown it too holds adventures and secrets, you just need a way up there)
Rivalries (There's nothing like having rival to push yourself beyond your limits, be it a friendly competition or a challenge of (and possibly for) your life)
Brightvale University Affiliates (BVU may be considered where the best of the best are from but that doesn't mean there aren't other universities, academies, and colleges in the other lands)
Plot Aftermath (Going off the "Post Meridell-Darigan War" idea, what happens directly after the events of a plot? How do certain lands and characters settle and handle things once things have calmed down? Are there any repercussions and side effects? How do people pull together as a community to rebuild and heal?)
Neovia Victorian Gothic (Honestly any land could make for a good theme, so what make Neovai standout? A peaceful (but haunting) town in a middle of cursed woods filled with monsters and ghosts? How it developed a unique culture separated from the usual style of the Haunted Woods? It's definitely a place which attracts attention and mystery)
Weird & Wonderful (Neopia has a lot of that. I'm not just talking about "weird" and "wonderful", I mean "WHAT IN THE WORLD IS THAT?! I'VE NEVER SEEN ANYTHING LIKE THAT BEFORE! MY EYES ARE WIDE OPEN, EARS HUMMING, JAW IS TO THE GROUND!" sort of thing)
Sidekicks & Partners (Sometimes one just ain't good enough. You need a team with members of different skills to cover weaknesses, watch each others back, and work together to achieve your goals be it winning a competition or saving the world)
War & Battle (War, war never changes. Neopia had plenty of them, both organized and fighting for survival. Stories of horrors, triumphs, winners, losers. How it happened, what happened during, and how it ended (though I think we keep what happened after for "Plot Aftermath"))
Royalty & Leaders (With so many fantasy lands Neopia has quite the amount of Royalty. Of course each land need its own leader and we got plenty of those too. Overall an issue about those in charge)
Stealth & Recon (There's a lot that goes on behind our backs and we're unaware of. From petty crimes to issuing a new world order, there's someone or some group out there plotting, sneaking, observing. And you'll either find out too late or get involved something over your head)
Slice of Life (You know you don't need to be a hero to have an adventure, sometimes a normal day can lead you to new places, things, and experiences which change your view of the world as much as a big plot did)
Magic & Curses (Neopia is filled with magic and the fantastic, for both good and ill)
Neoquest (Two of the most popular games at the time, its Neopia's version of a (mini) grand RPG to the open ended NQ1 or the more story focused NQ2 (or maybe you like the text-based "NQ3"
))
Petpets & Petpetpets (They're our pals (and the pals of our pals) or a menace (or a menace of our pals... or a menace of our menaces), the Petpets and Petpetpet
pets are a Neopian staple so why not give them some love. PPL approved)
General Winter (Winter some may feel is the strangest season. Its a time when it feels life slows down, some things shutting down or dying, it gets colder than can be tolerated, water freezes into solid ice, and white flakes falls from the clouds and covers what's beneath in a blanket of white. Yet, it also feels like a mystical time, the cold and emptiness showing a more quaint and peaceful side of things. Life still goes on, people working and playing, dressing warmly to go outside and at home getting comfortable being both happy to be out of the cold but also appreciating the quiet time it has given. Finally its during this time major celebrations are held, to be thankful to one another and cherishing good times. While we probably wouldn't focus much on these celebrations, the fact they happen during these times shows how we respond to Winter)
Scandals & Rumors (With so much stuff going on in Neopia its easy to forget consequences of things or things you hear may not be true)