Tbh I feel like the region hopping theme of this series was due to the upcoming 25th anniversary and thus wanted the anime to not be a one region exclusive while the plot is related to the new region but also the other regions. I wouldn’t really see much use of this formula post JN, everything relating to JN from Goh to the PWC will likely end when time’s up (whenever that is) since you can’t really do much more with the PWC if you have Ash beating the whole thing unless they want to drag it to the Gen 9 region which tbh I’d rather not see that and is kinda of a bad idea and despite the goal, Go isn’t really suited to continue on and will likely leave the main cast like every companion has.
That isn’t really true as if you look at how Goh is built his character is more built in a long term sense. Also Goh isn’t a companion, he is a protagonist along with Ash, so you can’t really use how past companions work as a example of how Goh will work.
Also they could have just used the Galar region as a hub if they just wanted the globetrotting to last only one generation. The fact that the hub is Kanto makes it more plausible that the Globetrotting is could last more then one generation. They don’t necessarily have to have the PWC be what Ash’s is focus on doing in future generations as they can just make something up.
Plus considering that there is anniversary for the entire franchise every 5 years and between them there is even anniversary for other generations of Pokémon games they would have an incentive to keep the globetrotting going.
One thing is for sure nothing is certain right now when it comes to what they will do for gen 9. At this point Goh is just as likely to stay as he is to leave, point being is that the globetrotting ending and Goh leaving isn’t as likely as your trying to make it sound.
Nor is the opposite anymore likely. The reality is it could go either way, we just don’t know.