Pokémon Red & Blue managed to squeeze 151 Pokémon into a Game Boy cartridge, which was an incredible feat for the time. The number of Pokémon has steadily increased over time and the developers managed to keep every Pokémon in the mainline games until Pokémon Ultra Sun & Ultra Moon.
Pokémon Sword & Shield will be the first mainline entries to not have every Pokémon, as the National Dex is no longer a thing. There has been a vocal backlash regarding the cut Pokémon in Pokémon Sword & Shield and it remains to be seen whether Game Freak will be spurred into action for later games in the series. The question that many fans are asking themselves is whether the National Dex is really gone for good?
The Official Comments Made By Game Freak
The task of revealing the news about the National Dex fell to Junichi Masuda at the E3 2019 Nintendo Treehouse event. Masuda said through a translator that Pokémon Sword & Shield would only allow gamers to transfer Pokémon from services like Pokémon Bank or Pokémon Home if they were part of the Galar Pokédex. An undetermined number of Pokémon would not be returning for the first mainline console entries in the series, as they weren't going to be included in the Galar region.
The backlash to this announcement was instantaneous and it has overshadowed the discourse surrounding the game since E3. There are some fans who believed Game Freak would cave and promise to add the missing Pokémon in DLC updates, but the company has stood its ground and no new Pokémon will be added to Pokémon Sword & Shield.
The most recent comment on the matter came from Masuda during an interview with Game Informer, where he said that cut Pokémon will return in future games. It will also be possible to capture them all in Pokémon Home.
The question that fans are now asking is whether all of the Pokémon will ever appear in the same game again?
The Addition Of New Pokémon (How Remakes Can Help)
The older Pokémon titles have steadily been remade and released alongside the new games, with Pokémon Diamond & Pearl next in line for the remake treatment.
The Pokémon remakes generally don't include many new Pokémon, if at all, which can be a tremendous help in giving Game Freak the breathing room needed to flesh out the Pokédex. If Pokémon King Diamond & Pearl Jam are next in line, then the developers will have a chance to add more Pokémon without the pressure of also needing to create new ones. The inevitable Pokémon Diamond & Pearl remakes could give Game Freak the chance to fill out the Pokédex, or at least complete enough of it to allow the next games to finish the National Dex.
The rumored number of Pokémon in Pokémon Sword & Shield suggests that Game Freak could complete the National Dex if given at least two more games worth of development time. It's likely that the last set of Pokémon games on the Nintendo Switch could sell themselves on the fact that they have all of the Pokémon from the series, even if it's only for one last time before the transition to the Nintendo Switch's successor.
The Problem With Mega Evolution & Dynamax Pokémon
The discourse surrounding the National Dex overshadowed the reveal that Mega Evolutions and Z-Moves won't be returning in Pokémon Sword & Shield, even though there is less of a reason for their removal.
It's likely that Game Freak wanted to remove these elements of the series for balance reasons and to keep things fresh. The new Dynamax power-up feels like a reworked version of Mega Evolutions, as the transformation lasts for three turns instead of the entire battle.
If the Dynamax transformation and Mega Evolutions existed in the same game, then the battle system would become overly-crowded with mechanics, especially if Z-Moves were thrown into the equation. It's possible that Game Freak will introduce new special mechanics in different generations of games and leave old ones behind, with Dynamaxing potentially facing the cut in a few years' time.
It's possible that Mega Evolutions could return in a future game, but only if Dynamaxing & Gigantamaxing were removed, meaning that forms would be removed in the process regardless of which made it in.
The End Of Catching Them All Is Inevitable
The Nintendo Switch is still early in its lifespan and it's likely that several more Pokémon games will be released before the end of its run. There is a good chance that there will be at least one generation of Pokémon games on the Nintendo Switch that has every Pokémon, but the end is coming for catching them all. The number of Pokémon will continue to swell and the difficulties brought by trying to add them all will only increase.
It seems that Game Freak is using the transition to consoles as a natural way to create the new status quo of the National Dex being gone for good. The Nintendo Switch will likely bring all of the Pokémon back for one more game, but the chances of that happening again in the future after that are slim.
Source: Game Informer