I'm amazed, you managed to sum up all my thoughts at same time :pUntil we see how they handle the Gen 8 games we can't say whether anything from Let's Go has influenced the core series. Though they consider it part of the main series I think we'll see them say it's a parallel to the core series. So in other words we have two (maybe three) subcategory of maine series games: Core (and if you want have the Remakes be it's own subcategory) and Let's Go (if successful and they continue it; though if Let's Go isn't successful and they don't do anymore it may as well be shoved under the GenVIII umbrella as a small little oddity/experiment). That all said, if they do decide to implement anything from Let's Go into the core series I don't think we'd see it until Gen IX as Gen VIII is probably well into production to make any major changes to its mechanics.
That all said, I am seeing SOME things I wouldn't mind appearing in the core series. Many have been wanting following Pokemon back, and its a cool idea for the bigger ones you get to ride on them. Also, while I think there should be normal wild encounters, I think it'll also be a neat idea for us to see wild Pokemon on the field (maybe after submitting them in our pokedex). And there's the idea of Pokemon wearing clothes which seems intriguing...
I still don't get the doomsday calling over PLGO, we already got the confirmation that gen 8 games will be the traditional core rpg experience, as someone said with uncalled rudeness, large majority of this thread has become useless complaint from people who haven't even bothered to read the interviews at all.
For what I think, PLGO will simply be the Coliseum/XD of gen 8: kinda like a main series game with significant deviations from the main mechanics, but which will ultimately remain a thing that stands on its own feet.
....plus my 2 cents is that they called it "main series" simply as commercial maneuver to get people buy it after the terrible first impression it had on buyers.