There seems to be a misconception that ratings for movies and other media are based on "maturity", like an 8 year old wouldn't pick up the meaning of the messages that are contained in the plots of Platinum or BW. And maybe that's true, but the 8 year old still can play and fully enjoy the game.
The ratings look out for factors such as:
- excessive violence
- sexual content
- tobacco, alcohol, drug use
- the "isms" and phobias such as racism, sexism, homophobia, etc...
- cursing and other strong language, especially when directed at a sort of minority group.
- and other stuff that violates societal norms, such as bullying. Usually a villain can get away with it but a hero or protagonist cant
You can produce a great movie or video game or TV show with a good message and your rating will still be the "E" or "G" rating. It is only when you start slipping in visible content that you start strattling the line between "G" and "PG". And at this point, there already is a lot of suggestive content in Pokemon games. Sure, a lot of it gets eaten up in localization, but not all (just go to the Ferris Wheel).
Looking at that list, the first four have never been a core part of Pokemon. Ever. Period. Remember, Satoshi Tajiri really specifically wanted to make Pokemon "faint" rather than "die" or "lose a life" because he thought that aspect of video games degrades life itself and makes us as humans respect it less. The anime and games typically go to great lengths to show that Pokemon battles are typically non-lethal and that 99.99% of the time, a Pokemon acting "evil" is usually because it is being mind controlled by some evil dude.
Even societal norms such as bullying and stealing can sneak in as long as it is done correctly. Silver, for example, never steals anything "on camera" and he later reforms his character. The newest rival has rage issues, but it is a plot point and he grows as a person in the story.
Can Pokemon push more boundaries with plots? Sure. That'd be great. The good thing about stories like Pokemon is there are layers everyone of any age group can take from. But that has nothing to do with a "higher" rating. Anyone advocating for a "higher" rating is pretty much asking for Pokemon to become their personal slash-fic/FPS or whatever, and in that case, they're better suited playing something else they'll enjoy rather than hoping for something that'll never come and was never intended to be.