I counted five lines. Six if Sylveon is added. You’ve got the Mime, Clefairy, Marill, Ralts, And Togepi lines.
Snubbull could still get snubbed...?
One problem with having many Pokemon outside of the first four generations is that not many in game trainers will use them anyway. This is a hard point for me to explain, but I'll do my best. One of the aspects of the Pokemon is not only you get to use them, but your opponents get to use them as well. Having too many Pokemon outside of what the opponents use would be a bit imbalanced. Even in FR/LG, HG/SS, and OR/AS, they had limitations on what you could feasibly use before trading before you got the National Pokedex. Personally, I feel like if it does extend past the first four generations, we will get a few others in this game like possibly Sylveon.
Now having said that, I'm still not sold that we are only getting the first four generations.
Here a point of ambiguity: Did this Facebook account erase the message because it was too early, or incorrect.
It is too early to know for sure. In the mean time, just trust the information that is out for right now.
Something pointed out earlier is that at this point, there are less than 100 species between Generations V to VII still not available this generation. A large amount of those are starter Pokémon (with no Generation V or VI starts available yet, that's 18 Pokémon, though it will drop to at most 15 when Oshawott is made available in
Pokémon Legends: Arceus). Considering very few NPCs use starters anyway, I think it's a manageable amount, especially if it's split evenly between
Brilliant/Shining and
Legends.
There are also very, very few trainers in Isle of Armor and Crown Tundra; nearly all of the returning Pokémon are not used by any NPCs at all besides AI teammates in Dynamax Adventures. For that matter, Legendary Pokémon are almost never used by NPCs. The first ever NPCs to use Legendary Pokémon were the Frontier Brains of Sinnoh; the first ever one with story relevance was N in
Black and White. After that, the only other NPCs in the main series to use Legendary Pokémon were Ghetsis, Lysandre, Hop, and Mustard. Mythical Pokémon are not used by NPCs at all. I don't think it's that big of a concern for them for the player character to have a wider amount of Pokémon than NPCs.
That being said, no one is saying that you'll be able to use post-IV Pokémon before some certain point in the game. It's always been a reward, of sorts, for the enhanced remakes.
Something that would be interesting, however, is if they not only opened up Sinnoh Underground, but also areas where you ordinarily got Mythical Pokémon.
Omega Ruby and Alpha Sapphire did what I thought was something pretty interesting by offering Deoxys to everyone who played the postgame by making it story-relevant. I'd like it too if they expanded one of the many Mythical Pokémon locations in Sinnoh to allow you to get more Pokémon there once their stories are over. Though Arceus is unlikely due to it being at the center of, well,
Pokémon Legends: Arceus, the very top of Mt. Coronet would be a logical location to put Minior, for instance.
They could make a workaround. If they are focusing on Sword and Shield as a main competitive format and don't want remakes to be the competitive format for a few more years then bring back the ALL OF THE missing DEXIT pokemon into a new Sword and Shield update so they can be used in online competitive there. Problem solved.
I have a hunch that this was their long-term plan from the start. I remember people noticing that Generation IV Pokémon in particular seemed to be missing from the base game for
Pokémon Sword and Shield, and currently, every Fossil Pokémon has returned except for the Generation IV ones, and every Mythical Pokémon has been made available except for the Generation IV ones. By the generation's end, I predict all the gaps will have been filled in.