I feel the urge to share one of the things I commented on the Pokopia subreddit here. (Note: I haven't played a game and I've only watched like the very beginning of the game, I am not fully sure on all locations)
"If The Pokemon Company weren't cowards they'd do Cinnabar and add a Missingno reference. Have it be subtle, like you could find a Kabutops or Aerodactyl skeleton/fossil stuck in the east coast that you need to thaw. It'd be a "if you know you know" reference."
(context: the post was talking about there being a frozen island for ice types which apparently are not in the game and they said it'd be Cinnabar or Mt Silver)
I've got no interest in Pokopia myself, but that'd be a fun idea! I really wish they'd reference MISSINGNO. more, but at the same time I understand why they don't.
I'd like to use this ask as a chance to ramble about my own thoughts about MISSINGNO. being officially referenced (or rather, why it isn't), if that's alright! I just have a lot to say about this subject in particular.
I don't think we'll ever know the reason why The Pokémon Company want to keep MISSINGNO. out of their games, but it seems to me like they're afraid to imply that MISSINGNO. is a canonical part of the Pokémon world.
If they were to allude to its existence in the games even slightly, they might be afraid that fans would immediately blow it out of proportion by assuming MISSINGNO. is a canon Pokémon and that the cameo is a hint towards it appearing in future games - when in reality, they have no intention of doing that.
While we as adults adore MISSINGNO. in retrospect, MISSINGNO. is unfortunately a very controversial mistake of Pokémon's past. Back in the day, it scared many younger kids and broke their immersion of the world.
By officially acknowledging the nature of MISSINGNO., you'd have to admit that the world of Pokémon is nothing more than a game, and not a living, breathing world. And I think they want to do everything in their power to prevent that.
Since then, they've taken great steps to avoid anything like MISSINGNO. happening again. I don't mean that there's no more glitch Pokémon, but their appearance has shifted into something a lot more uniform and palatable in the modern day.
Ever since the 3DS era, all glitch Pokémon have had a placeholder model of a Bulbasaur or an Egg.
We don't have garbled sprites like MISSINGNO. or DPBox anymore, we don't have strange-looking placeholder sprites like Decamark anymore. It's all just Bulbasaur and Eggs. So that way, even if a kid somehow found these glitch Pokémon by accident, it wouldn't scare them as badly, because they still look like Pokémon.
Another reason might be because MISSINGNO. wasn't actually as accessible in Japan.
The infamous Cinnabar-surfing glitch that we all know it for was actually only in the English/European versions.
And while Trainer-Fly existed, you couldn't find base-form MISSINGNO. through it, because MISSINGNO.'s Japanese front sprite crashes the game.
While there are some more complex methods to obtain MISSINGNO. in Japan, MISSINGNO. clearly got its claim to fame through English fans due to how much easier it was.
And since these games are developed in Japan, the English side of Pokémon doesn't have as much of an influence on how these games are developed. They only really influence how the game is localized.
All of that might be why the only official nod we've gotten to MISSINGNO. has been in an English YouTube video.
On April 1st, Beyond the Pokédex's Magmar episode made some surprisingly direct references to it!
But even then, they didn't address MISSINGNO. by name or show it off directly.
And I think the most damning reason for that is because MISSINGNO. can't be copywritten.
While it was named by the Pokémon devs, its name isn't trademarked. And its original sprite was technically computer-generated, which means it can never officially appear in its most recognizable form.
Pokémon can never explicitly name or show MISSINGNO. because they cannot own it. They don't want to imply the existence of a Pokémon that they cannot have legal ownership of.
Sure, they have ownership of its fossil and ghost forms, and if they wanted to tease MISSINGNO. through the use of those three, they can -but they can never say its name because they don't own it.
Which is really sad to think about for all the hardcore MISSINGNO. fans out there who are begging for it to be acknowledged more.
I've made my peace with it personally - I don't expect Pokémon to address MISSINGNO. directly, but I'll be pleasantly surprised if I turn out to be wrong. The Beyond the Pokédex episode is proof that they're not forbidden from referencing it entirely, so we'll see if it gets alluded to again someday in the future, no matter how subtle!