https://www.serebii.net/swordshield/galarpokedex.shtmlHow will they release the remaining Pokémon?
When Ruby and Sapphire were released with only 200 Pokémon, they released FRLG later to fill the gap.
Of the 58 evolutionary lines returning that are on this list, 6 are from Sinnoh, which is not far from the expectation (8,3 per region average).
There's apparently no lack of Sinnoh Pokémon to justify Diamond/Pearl remakes, so what?