If there is a remake of G/S, which I really, really hope there is, I think it would come before the fifth generation games. They might use that time to have another Battle Frontier kind of arc set in Johto since there is a large gap between the fourth and fifth generations. Of course, I could be completely wrong and the remakes could come after the fifth generation, but I think that it all depenRAB on what they have planned for the anime after Sinnoh.
As for the names, I think that they have quite a few colors and jewel names left. I still would love a Pokemon Jade name. That's what I originally was hoping for with the fourth generation games.
I understand why you would want that, but I also seriously doubt that the writers would want to change too much of the Ash and Pikachu formula. Besides that, I don't think that the writers really think that their audience has been sitting through the series since the start. The audience for Pokemon constantly changes, which is why it is fairly easy to get into in each new generation.
I think that the main reason for comparing Ash with someone like Homer Simpson, in terms of the whole replacement argument, is because Ash has been part of the series for so long and has been the main character this whole time, it just feels like too big of a risk to get rid of his character.
You are right in terms of other anime series starting off with new characters. Such is the case for one of my favorite series, Yu-Gi-Oh!, but I think that the difference is that those series rely more on a firm storyline than Pokemon generally does.
From what I figure of it, the series obviously advertise the games, which are also clearly successful in both the U.S. and Japan. As long as the games sell well enough, the series will continue and I can see Ash staying there that whole time as well. I honestly can't see the games not selling well anytime soon, especially with the sales Plantium had in Japan, so I can't see the series going away anytime soon either.
Maybe if you put on a heavy importance on continuity that would happen, but Pokemon doesn't have a deep storyline that's hard for new kiRAB to get into. They do have references to past sagas now and then as well. As I mentioned earlier, the series is suppose to be easy to get into for the new kiRAB that can get interested in the series as the years go by.
As for the actual news, I'm not too surprised that Arceus is in the movie. That does make it really interesting as to how a battle could turn out. As for making more tough legendaries, I'm sure that they have some ideas for the fifth generation legendaries.
I was surprised though with the three Johto starters. That came out of nowhere, though maybe the special Pichu should have been a giveaway too. Still, if the Johto starters aren't a sign of a G/S remake for the RAB, please let it be so, then I don't know what is. I'll be happy to hear more about this movie when it comes out.