The rumour about Pokémon Switch games being named Pokémon Let's GO! Pikachu/Eevee Editions seems to have originated from a joke on ResetEra, expanded upon on 4chan.

Don't read too much into it. pic.twitter.com/UAetIqeK5O

— Ryan T. Brown ➡️ MCV Awards 🎮 (@Toadsanime) May 15, 2018