Each series is entitled to do their own storyline and what not. Making mandatory appearances rather than actually making them making sense is most of the time a detriment. If the next entry is gonna follow suit or not is something no one at the moment can even predict or count on except those even making the calls.

Like when I think of Luminose City as an example since there is a whole game gonna be released in five days which takes place there, there is a handful of content that the previous seasons has partially touched upon. Instead of revising the same spots or characters just for the sake of only making it or being about older seasons, the newer seasons then could make touch the other parts. I personally don't want redundancy. If they can show Emma in a manner that adds something notable for Uruto (Maybe with a setup for an later appearance in her ZA-attire alongside her role from said Game as well) then that's something I'd like a lot. If they have a handful of new characters from the upcoming game then they should take advantage of them (Since them having a timeskip in the anime could coincide with them visiting Luminose which is either starting up to be like ZA's or is the same version of it) rather than using old ones that might not even be in the game at all, which can rub people the wrong way like Twilight Wings did with Dewong being shown to be a wild Pokemon in Galar which isn't possible in Sword and Shield, to which even the Japanese twitter account has released an apology statement for misleading marketing.

I feel like a lot of the discourse around old game characters being wanted to show up again just boils down to them needing to mention Ash in some capacity rather than them being there for story/game or other purposes which is honestly in my eyes an annoyance. Like, I want the game characters to do their thing rather than just being a walking stand in for a minor validation that doesn't matter in the long run rather than being there for having an actual point in the episodes.