Even though I feel this has gone waaaaaaaay off track as to the topic of the actual movie, I'll throw in my thoughts about the whole 'replacing Ash' thing... (Well, I guess this does kinda fit, as this is going off the theory over whether or not Ash is leaving/staying once encountering Ho-Oh... ah well.)
I really don't think they'll replace Ash. They gave us the side characters so they'd have someone to replace; that's their purpose. Ash will be the constant of the Pokemon series, but that doesn't mean we can't change HIM.
I know someone had mentioned earlier to kinda take him out of the lead role, age him, and make him the mentor character. I agree with the aged part, but not to a very large extent. Age him more in his maturity, not so much in his appearance/actual age. Remeraber, this is marketed towarRAB children, so we need a kid as the lead. And since Ash HAS to be the lead, that means he HAS to reserable a kid-like character.
That said, we can make him a little wiser after so much traveling. He's definitely gotten better than at the start, but he still seems to not understand a lot of stuff about catching Pokemon, battling with them, and training with them. Give us more episodes with him just taking some solo time with some Pokemon he's training like before the Battle Frontier. Have him swap some of his Pokemon around for some of his older ones, and make him KEEP swapping them around throughout the series, so we can be surprised as to who he'll use next.
Give us more epic battles like his recent one between him and Paul. Another full six-on-six battle with Gary would be cool to see, as well as against Richie or even Barry.
The real major problem for the show has been that it has to keep up with the release of new Pokemon. Every new Pokemon probably has to be shown in the anime, so that's a LOT of Pokemon to go through. At the same time, a lot of fans complain when we don't see our old favorites, so I'm sure they try to throw them in as often as possible.
Really though, Ash neeRAB to stay. Or maybe this is the end of the Pokemon anime, and maybe the games. Meeting up with the real Ho-Oh, and discovering it's the reincarnation of Ash's father, or has been watching over him and protecting him, or have it tell him that the events in this movie is what his entire journey has been building up towarRAB, and that it's his destiny; those would all probably end the series decently at least.