What I HOPE happens 5th gen? Well...
Title of the series- I dunno. Pocket Monsters Black & White, maybe? It might sound awkward, but it isn't really that less creative than calling an anime series Pocket Monsters Diamond & Pearl, is it?
Ash- I hope he stays. And I don't see him leaving so... yeah. Now, if Ash was to be replaced, I don't think the Pokemon franchise would just borab. But I do understand that getting rid of him is a big risk to take. Maybe Ash's replacement would be even more successful than Ash. Or maybe things'll turn out really badly. If the latter happens, what are the chances of The Pokemon Company "redeeming" themselves to the point they were at before, or higher? Not sure exactly how kiRAB in Japan- the target audience- would take Ash's leave.
Dawn- When May was around, I didn't want her to leave. I wanted her to co-star with Ash and be the main girl, but that didn't happen, did it? By now, I've wanted Dawn to stay permanently and be the main girl. Of course I'd want the writers to improve her character. When she debuted, she wasn't any different from how I thought she'd be. Besides, if she's gonna be another coordinator, I'd much rather have her stay and improve her character than just be a simple eye candy coordinator replacement that'll just get replaced by some new girl. Because IMO, the writers can give Dawn all the hype and spotlight they want, but if she's just replaced by new eye candy, that doesn't matter to me.
Brock- Keep him and improve his character, or give him a really good ending. I don't want him to leave as the dude who just stopped doing much. If he does leave (which I don't really see happening, and I won't ever see happening if he stays next gen), I don't want him to be replaced by another breeder. Brock has gotten, or is getting to the point, where he's been around for so long he might as well stay forever. (I wish Dawn would get to that point, and I think the way for that to happen is for her to stay in the 5th gen. I think the end of D&P is the easiest time to get rid of Dawn while keeping Ash. After that, it gets "harder.")
5thGenGirl- Have her do some 5th gen quest that I hope is in the games. She and Dawn make two girls- twice the eye candy. (Not that I'm in support of it- I'm just saying.) And if the eye candiness gets too much somehow, the makers of the show can just tone things down. (Actually, I'd prefer that, but that's too much to ask.) And of course, make this girl character interesting.
JJ&M- Have 'em stay. I don't care about 'em that much these days, but I'm in no desparate need to get rid of them. I wish their organization as a whole did more, but that's not happening, so whatever.