On the earlier topic of Vergeben's sources possibly mistaking an Isaac AT for Matthew, I'm heavily skeptical of that being the case. However according to Vergeben's words, the source that erroneously claimed Isabelle was an Echo did so after seeing some footage of her and assuming from there with the similarities to Villager she had, without being knowledgeable enough to distinguish between an Echo and clear semi-clone. So considering that I suppose it's possible the sources that claimed an Isaac AT saw a golden spiky hair boy pushing people with a big hand and immediate made the assumption it was Isaac without distinguishing if it was Matthew first.
But then a Matthew AT would have to exist alongside playable Isaac in the first place for that to be a possibility, and I'm very doubtful that Sakurai would do that. However obviously Isaac's AT move wouldn't carry over to his playable form without being nerfed into pretty much an entirely different move, so it could be possible that Sakurai made Isaac playable yet found his old AT's function to be investing enough to bring back with a nigh-identical but technically different character while simultaneously giving a boost to Golden Sun's representation.
It's definitely not a prospect to get your hopes up over, but it might not be impossible.