I looked further into why it's only 20 episodes, and turns out that's the standard size order for every Nick series. They only order 20 new episodes of their shows a year. I think we've just gotta get used to it. That said, they do like to have TV movies, so even if Episode 20 is open-ended, they'll probably wrap the storyline up properly with a special. Or if it really is a successful season, they could top up that order with another 10 to 20 eps, who knows.
PR being "2 years" behind Sentai is a good thing imo. It means the show can properly structure its story around all the Sentai footage, and plan it all properly. And actually, Shinkenger only just wrapped everything a few months ago, so although they're 2 broadcast years apart, production time is much closer together.
