According to a leaker that revealed information about Sword & Shield, the final evolution of Sobble would be based on spies.
And that would not be a stupid reasoning, one can think that the starters of Galar will have common theme of British culture, and espionage coincides with this theme, because who is the most famous spy in the world ? 007 James Bond ! Which is part of the British culture. Besides, it's funny, because Sobble is the number 007 of the Galar's Pokedex.
And if I combine James Bond and Smash bros, we find the interview of Sakurai where he expresses his desire to put James Bond of Golden Eye 64 in Smash. So the inclusion of Sobble would be a little revenge for Sakurai.
Plus, it could be easier than it is thought to include! From a distance, Sobble is close to another starter ... Froakie. 2 animals with a close look, with a long tongue and whose final evolution is a specialist in infiltration, one is a ninja, the other a spy.
You see what I mean ? The final evolution of Sobble could be an echo for Greninja. After ... If the Sword and Shield representative is an echo, this may leave room for Decidueye to be in the game with some original gameplay, but that's a lot too fancy.