>>50417883Since gen 6, pokedexes are typically 400 pokemon, not 150. Outside of remakes, the only game post gen 5 that's less than 400 pokemon is PLA at 242, which is why so much of the region relies on repeating pokemon and evolutionary lines showing up in every section in different stages.
If SV went with 150, with the fact that it's confirmed to be a large open-world map (meaning larger than PLA's map), having such a tiny amount of pokemon will mean extreme repetition to try to inflate the population. The only way we'll ever get a new game of ONLY new pokemon is if it's either a tiny region or spinoff, or if we get a new game that introduces 400 pokemon (which would also likely mean no old pokemon can be used PERIOD due to dex stuff.)