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A random thought:
I think they will never update the graphics of remakes again and with that in mind Unova will likely be their last remake
The keep point is mainline series are getting smaller in scope each gen since gen 5 with the next iteration only bringing in less features, less gameplay, smaller maps and overall demanding less time to beat the main story with a non existent post-game content
I mean, to make a full remake Pokemon Platinum with current gen graphics and maps you need to actually spend money and time. Sword and Shield have weird small lazy maps with boring routes and so on. Sinnoh is a bigger region with bigger story, more monuments, more designed geography, more cities, more story to animate, etc etc, the cost and time to make Sinnoh with Sword and Shield level of graphics would need more money and time than Sword and Shield to a potential smaller seller
Game Freak clearly doesn't care for quality, they want to maximize profits with a inferior quality product. This remake will sell over 10 million copies regardless of what it looks like, so why spend 5x their budget in a game that have a ceiling of sales under Sword and Shield (around 20 million copies)?
Mainline pokemon's are more expensive because they start a brand new generation, it's not only a matter of graphics and manpower, it's about keeping the brand alive even with the bare minimum technological progress. Remakes doesn't need such effort, their main goal is to exploit the brand
That's why I think Pokemon Legends may be their next iteration of secondary series after the mainline Pokemon, if it enjoy a good success enough to justify a sequel to be released I can see them fully dropping remakes to favour this new series.
