I disagree entirely. I do not nor have I ever liked Pokemon. By the time that craze hit, I was already well outside the target demographic for the cartoon and the cards never interested me as they simply seemed to represent a "Magic: The Gathering, Lite", which, considering I had recently decided I had better things to do with my time and money, held little appeal. When the video games rolled around, I could care less but did eventually give it a try on the GBA just to see what all those crazy kids were going on about. As a result, I think I can at least look at the issue without bias as an entirely uninterested observer.
First, if we assume that the card game and the series (and movies I suppose) represent the "canon" of the world, what we have is a world where children will, out of an obsessive compulsive drive I assume, collect dangerous monsters that can be placed into spheres that contain extra-dimensional space and, presumably, some sort of brainwashing apparatus. Monsters can be collected by having other monsters do battle with them until they are sufficiently weakened that our extra-dimensional brainwashing spheres could contain them without a fuss. The monsters, like normal fauna in the world, have a predator and prey relationship (in that there are monsters that are clearly carnivores and others that are obviously herbivores) yet even the monsters that would normally be classified as prey tend to be dangerous in certain circumstances. The actual relationship between the various monsters sets up a rock paper scissors relationship between wide classifications of entire monsters where one type is effective against another but vulnerable to a third. Also, different monsters tend to populate specific regions and the population of any one monster type is probably different than another. Presumably, again because of the obsessive compulsive nature of the average "trainer", these rare pokemon are especially sought after. A trainer is so called because they simply shove their pokemon into battle against others time and again in order to teach the creature how to respond in a variety of circumstances and, since death is apparently impossible in this universe, even failures offer the opportunity to learn. It is often true that the best trainer is therefore the one that spends the most time training as the actual method used in the process is largely irrelevant. When any two trainers meet, tradition dictates that their respective pokemon do battle. Presumably in a nod towards fair play, any given trainer is only allowed to field a stable of roughly equal size as his opponent. It could also be that extra-dimensional technology does not extend to backpacks and pockets and the stable size is dictated by the number of large spheroid objects one can comfortably carry.
The video games, it would seem, capture this quite well. In any given game we have an established villain. Given that the premise of the series is the capture and abuse of various flavors of monster, and that death is all but impossible, the villains tend to resort to cartoonish villainy in order to actually seem worse than the player. Any given game also tends to feature a jealous rival (who may or may not be the villain), in order to have sustained conflict as the game drags on for hundreds of hours. The basic premise is that a player will gather pokemon (a nod to both the show and the collectible nature of the CCG), and "train" them (a process that goes hand in hand with collection for the most part), and will occasionally do battle with other notable trainers (gym leaders, the villain, the rival, etc). This more or less describes the arc of any particular segment of the pokemon series one chooses to examine.
Since the basic formula is all but set in stone by the canon itself, that leaves little room for gameplay innovation. Simply changing out a creature list by including new creatures with different attributes changes the metagame inherent to building one's "fighting stable" (that is, the creatures the player actually uses from battle to battle). If one adds or subtracts entire types of monster, the metagame is changed enormously as the basic balance of power is altered as a result. The story itself is largely impossible to change without altering the tone and premise of the universe itself. One could explore the reason why a particular trainer chooses a grueling life of pathological animal abuse, but the result would almost certainly either trend towards the entirely absurd or be far too dark for the young target audience.
The game itself has always been little more than a time sink and it's most basic mechanisms favor grinding above any pretense of skill or strategy. A player's goal is, ostensibly, to defeat various trainers until they reach a final tournament. These encounters act as "gates " of a sort where a player will be unable to pass until they either have a stable of sufficient level to simply overpower their opposition, of sufficient synergy that they can overcome their opponents, or some combination of the two. It is these gates that enforce the grind. It is in the metagame itself that most of the strategic challenge is found as one obviously cannot build a stable that offers a solution to any particular tactical conundrum, and a player is instead expected to provide a working stable that offers a solution to the widest range of likely encounters. This is similar to the nature of the CCG where the build of one's deck determines what sort of scenarios a player has an inherent advantage, and the actual tactical portion of the game offers relatively few options at any given moment. In the videogame, at any given time in a battle, a player has but six choices available to them on any given turn: use one of the four attacks (a choice that is, itself, self-limiting as it is likely that a particular attack is most effective at the moment and this effectiveness is based upon the opposing pokemon - thus this choice is largely based on random chance or, more likely, upon knowledge of the metagame itself), they can choose to use an item (one of the two actual tactical choices available to the player) or they can choose to switch the current pokemon for another (a tactical choice based largely upon the metagame. One would not want their fire type pokemon going against a water type for example, and thus switching is the obvious move unless there is a dramatic level difference). It would seem to me, then, that alterations to the metagame, something done simply by changing out the list of available pokemon and/or adding and removing types would be the change most likely to actually significantly alter the experience. It would alter, for example, the players choice of stable, the regions they choose to frequent, the attacks they would choose and so forth.
Each new pokemon game, generally speaking, must satisfy two requirements. First, it must appeal to some portion of the veteran audience, a group who, by definition, favor an experience that rewards grind as much as guile. Second, it must be accessible to a new group of 6 year old (and up) gamers which means significantly adding depth or strategic complexity is almost certainly out as an option. Each new pokemon game serves largely to target the new up and coming gamers. Some portion of the veteran audience might come along for the ride, but given that there tends to be one major pokemon release per platform (often split into several identical games with differing monster lists), the reasonable presumption is that, given the dishwater shallow nature of the narrative of the universe as a whole and the simple gameplay, only a small portion of the audience will stick around for the new version.
As such, I'd have to say that increasing the narrative complexity is hardly called for. The game is best served by including easily identifiable villains, heroes, mentors and stooges. Exploring the difficult concepts that the condition of the world implies is hardly necessary: do you really think a player wants to consider the moral implications of forcing these creatures to fight brutal battles day in and day out? Do we really need to understand why the conditions of the world are so utterly fucked that small children are likely to wander the wilderness in search of monsters? Do I really need to know that some pokemon are sentient (if I'm not mistaken, one of them posed a question considering its existence, a feat that implies self-awareness) In that vein, altering the way the game plays is almost certainly out of the question. Increasing the cap for maximum number of known moves for example would do little to alter the actual battle mechanics and would, instead, simply alter one's choice of stable - something that can be done by list switching.
Pokemon, in my mind, does not need to change what it does. The narrative and game complexity serve perfectly well for the audience being targeted and the franchise as a whole, just like every other property that targets children, simply seeks to increase the franchises mind share among children in order to allow for easier merchandising opportunities.
That said, if it were to change, the entire concept would need to be rethought from the ground up as only an enormous change in what we define as inherent to pokemon would actually serve to significantly alter the game experience.