In a recent interview with the great Junichi Masuda, the man himself stated that the Pokemon Company is looking to have Pokemon: Let's Go, Pikachu be compatible with future Mainstream Pokemon Games (and not just with Pokemon GO). He expressed that he doesn't want players not being able to transfer the Pokemon they capture in Pokemon: Let's Go, Pikachu to future games, similar to what happened back with the 2nd and 3rd Generation Games. This gives players hope that one day Pokemon: Let's Go, Pikachu will have this compatibility; however, this is anything but set in stone.