Oda has been setting up clone shit for a while now, so I expect that to come up at a certain point. Either because Shanks is a clone, the other Shanks is a clone, they are both clones or nobody is a clone and it's just "family". Though if it's the last case, we still have the question of why in hell was baby Shanks just chilling in a chest.
But yes, realistically speaking, outside of how Shanks baby ended up where he did, being clones, brothers or whatever is honestly irrelevant for the most part. I don't honestly expect Shanks to give a flying fuck if he's revealed to be a clone of Garling (unless there is some shit to force obedience, but seeing how Stussy was very autonomous and Kuma required years of processes to turn him into a mostly big puppet, I'm not banking on this one) and Luffy would certainly not care a quarter of a fuck as long as he can identify his Shanks.