I agree with Tomato, that they shouldn't make any new regions. They should just work off of what they have, like make a game about a contest coordinator, or about a Gym Leader. I think that Nintendo/Game Freak seriously jumped the shark with Sinnoh. I'm not saying D/P wasn't fun, but rather than making not enough new things, they put too much in, (mostly all the Pokemon that were probably created by 4 year olds) I mean, D/P was fun and all, but I was dissapointed in seeing Pokemon like Bidoof and Krickitune.
I think it's pretty obvious that Nintendo/Game Freak will make a new region, solely for marketing purpoises. But who knows. Maybe the fifth generation could be unique from the others, like for the Wii? ^_^