I've been scratching my head over what the next games could be for a long time now, and I still have no good idea. Some guesses seem more likely than others, but they all have some pretty substantial drawbacks that make them unlikely. Just to give a quick rundown of my thoughts on the most likely options:
(EDIT: For some reason, the text editor has become really bugged for me. Sentences appearing several times even though I've only written them once. Some spaces I can't delete, others I can't add. Sorry for any problems reading this post, it appears to be beyond my control. For instance, if I press Enter, the word AND appears in all caps.)
Sinnoh Remake: Perhaps the most widely expected one, but there are hurdles everywhere when you look at it closer. As
Worldie said, there just doesn't seem to be a way to do it right. Sinnoh's art style and route design doesn't lend itself well to anything other than a fixed top-down camera and orthogonal movements. But this would quickly end up looking like an upscaled DS game,which would be a tough sell to new customers. Pretty much the entire region (and it's a huge region!) would have to have a complete overhaul to look passable for a Switch game. There also doesn't seem to be an easy way to implement the Poketch, Poffins, Super Contests, or the Underground without that secondary touch screen. And Game Freak would want to include current-gen gimmicks like Camp and Dynamaxing,possibly Raid battles and Dens and all that,requiring further alterations. All in all, a Sinnoh remake would involve a whole lot of redesigning and reimagining. And for which demographic, again? It's been fifteen years since Diamond and Pearl. That's really too long to try to capture the nostalgia of the original playerbase. A six-year-old who played Diamond and Pearl at release would be 21 by the release of these games. That's way outside the target demographic of Pokémon. Even a six-year-old who got Platinum the week before BW hit the shelves would be 17 this year. I'd say it's too late for Sinnoh to cash in on nostalgia at this point.
Let's Go Sinnoh: It has only been fifteen years since Diamond and Pearl. That's really too little for the original playerbase to have had kids of their own to introduce to Pokémon, which was the selling point of Let's Go Pikachu and Eevee. Well, that and being the first Pokémon games on the Switch, I suppose, but that ship has kinda sailed as well. The graphics style of Let's Go - modernizing the original GameBoy style while also being a tile-for-tile remake - would be an enticing way for the designer to solve the graphics dilemma, though. But the other issues with Diamond and Pearl remain: There's no way to remake them faithfully, and then what would be the point of remaking them at all? Sinnoh as a region really isn't conducive to a Let's Go-style limited Pokédex either, since there are relatively few "Sinnoh original" Pokémon,and a significant percentage of those are related to earlier Pokémon by evolution or are legendaries. The Pokédex of a Sinnoh game would necessarily have to incorporate Pokémon from several generations.
Let's Go Johto: Again the issue of "you can't sell LGPE twice". LGPE had the nostalgia of "Pokémania" and being the first Pokémon games on the Switch as selling points. Neither are applicable to Gen II to nearly the same degree. There's also the interesting question of Unown. What to do with those now that Hidden Power has been removed from the games? I suppose they could all learn Psywave or something, but it really wouldn't be the same. Also, Psywave has been removed from the games too. Confusion, then? Yeah, good luck getting players interested in
that. Oh, and remaking HGSS? Those games had a scope Game Freak only laughs at today. No way they would embark on such a feature-rich project.
Sw2/Sh2: A follow-up of the first games of the generation. Just like we've had in every single generation bar Gen VI. Creating them would be easy, just copy over the first games and add some tidbits here and there, plus a gimmick to sell them well, and put the games on the store shelves. It's easy and convenient, but the existence of SwSh DLC makes it questionable whether it'd be worth it. In a sense, they have already sold us Galar twice (and it's not a very sellable region). Would they be able to sell it again? To be competitive with SwSh, they would have to have all the features including those of the DLC, and then some. Would adding all the Pokémon back be enough? A Battle Frontier? Sure, we'd appreciate it, but I'm not sure if it would sell well among the general public to justify its development costs or the inevitable hit to their reputation unless they made it
really good. And even then, they'd be accused of holding SwSh back so the sequel would sell better. I could see some potential for a good Galar game with expanded locations and more content and better graphics and whatnot, but overall I'm not sure how realistic that would be.
Generation 9: Until somewhat recently, I thought the most likely way forward would be moving onto a new region. It would be potentially less work than remaking Sinnoh, but with lessons learned from Galar and the freedom to make something new rather than trying to emulate something that already exists (and was designed within the limitations of an ancient system, forcing you to work with all sorts of awkward stuff just so it looks the same). Novelty also sells well.
However, it is a valid point that Generation 8 is still quite new, and it's too early to start a new cycle already. And a new region would warrant a new story, new characters, new Pokémon, new merch, all while there's still plenty of potential left in Gen 8. There also wouldn't have been a whole lot of time to design all the new stuff just yet. I don't think we're due for a new generation this year.
SwSh DLC3: One major question: what would be its selling point? The other DLCs have given us all the usual convenience upgrades and all the usual legendaries. There isn't really much left to sell. Still, some Pokémon are missing (no overly exciting ones, mind), and fans have always been clamoring for a Battle Frontier, so there is some potential left. I doubt there's enough for two sets of DLC, however, making this less interesting news than last year's news. Is that befitting of a big anniversary celebration? It would, on the other hand, beg the question of what the entire dev team has been doing since SwSh were released, since a DLC doesn't require that many people, generating some hype for the next games again.
So in total, every way I look, there just appears to be more arguments against every option than there are in their favour. Everything appears to involve an unrealistic amount of effort, be too hard to sell, or both.
If I were to make some sort of conclusion, I think a new region is unlikely, so it will probably be a remake of
some kind. I think the order of likelihood of regions in the next game goes somewhere like Galar > Sinnoh > Johto > New region > Other regions, but we never know.
Or, well, we'll know tomorrow.