How do you think that Satoshi and Pikachu is now replaceable when NOW the merchandise producers to obtain money need Pochama!!!! toys to help the franchise? Yes, I said Pochama because the toys companies want to find a place in the marketing listings for Pochama to appear in the toys since older pokemon were allowed again in merch.
This is a pokemon whose owner (considering that they are promoting Hikari's Pochama) and the pokemon itself only appeared in 9 of the 50+ episodes of the BW 2 Series. And this is from a pokemon that debuted in 2006, with a Gen IV starter and whose trainer is exactly the female protagonist of the DP games!!!!
And there's the issue that each time is more likely that the members of Team Rocket, Musashi, Kojirou and Nyasu are returning to have the ... OS/AG/DP perosnalities!!!!
If you think that Satoshi, after 16 years, is replaceable for another character, I don't know what I think of you.
It's obvious that the writers will prefer to reset Satoshi (calm, probably not in XY) than to leave him. The maximum that I see is sightly aging Ash but there's very unlikely.
And I have a very clear opinion about Ash and you (the users):
-If you hate Ash/Satoshi and/or Pikachu*, you should quit the Pokemon show off and not post in serious forums like here, Serebii and other serious sites. Specially the subforums that deals with the Pokemon show. I understand the hating of some rival but I can't accept a clear hate in the Pokemon anime forums to the main star of the show.
I think that this place is for discuss things witht the fans of the show, not with the haters of the show.
*And in the time of DP that also applied if you hated Hikari/Dawn.