1. Eh, maybe. A lot of people ask for this, but I have a feeling that once they had it they wouldn't like it. It would anchor Pokémon down to your living room. I don't think that game experience is meant for consoles -- imagine playing one of the existing games on your television, as opposed to at a friend's house with a group. What's the point? One of the biggest factors in Pokémon's popularity is its portability. If you take that away, if you make the game something that can only be played in your house, you take away arguably the series' biggest draw. This could be partly rectified by a Monster Hunter 3 Ultimate-type deal where you could buy both a home console and a handheld version of the game and transfer your save data between them, but that just seems pointless when most people will simply continue to play the handheld version. It could work, but there would HAVE to be a handheld version. Maybe make it so that the home version is the "Red" and the handheld is the "Blue" or something.
2. No. What, completely redesign all 700+ Pokémon? To accomplish what? Narrowing the series' base? I don't think so. Pokémon has a look that sells very well to a certain audience. Nintendo isn't going to be able to convince the Call of Duty crowd to buy into Pokémon just by making the mons more "realistic" looking.
3. Eh, some of these are alright, some of them are silly (take away PC storage? Really? Why?). Pokémon death can be (and has been) a matter touched upon in the story, but I don't think it should be factored directly into the gameplay.
The series has already gone the "older trainer" route in fifth gen... notice they don't really look older because of the art style. Everyone looks pretty much the same age in Pokémon unless they have grey hair and wrinkles. Anyway, making the trainers specifically 21 sounds like a ploy to appeal to players who can't sympathise with a character that is not the same age as them. Furthermore, this would alienate the younger audience that Pokémon thrives on. There is no shortage (NO SHORTAGE AT ALL) of video games starring adult men as the protagonists. Anyone who wants to play one of those has an abundance of games to choose from. Here we have one of the few series that employs a younger hero, and you want to age him or her up for no good reason. I wouldn't oppose more customization in the player character that allows you to adjust their age as you see fit, but I just don't see the point to forcing younger players to step into an adult's shoes in yet another game.
And your comments about the story. "You enjoy the thrill of battling and the money is lucrative. This is your motivation at first." "The trainer should have a grittier outlook on life to warrant his actions." No, no, no, no, NO. Have you even played a Pokémon game before? Ever? The games don't force a bunch of characterization and motives down your throat. YOU are the character. His or her motives are your own. Notice that Red, the only player character to reappear as an NPC in a later game, never speaks. This is to maintain his status as a player character, his role as an avatar for those who remember being him in Red, Blue, Yellow, FireRed, or LeafGreen. To make him speak would be to literally put words in the player's mouth. GameFreak clearly respects their own philosophy that their protagonists are conduits for the players, not characters unto themselves. This is a core element of Pokémon's design and has been ever since the series' inception. In truth, it more closely reflects the attitudes of Western RPGs than of their Japanese counterparts. Again, I would support further character customization instead.
One of the few ideas in the OP I can get behind is the suggestion to limit the player to the same number of Pokémon as their opponent. This would be an interesting mechanic to implement. Maybe offer a sort of difficulty setting at the start that incorporates this into the harder difficulty.
