To me, the tweet implies that sakurai was not the one responsible for making the screenshot. I was probably one of the bandai staff was a GS fan. But, it also implies to me that Sakurai is a fan of Golden Sun fan too, which surprises me so much. Not sure if it is a tease or not, but I am willing to believe chairs lead to Skull Kid now since Sakurai is allowing hints to be made for characters like Chrom and Dark Samus.
If Isaac gets in, that changes speculation for me. I thought for the longest time that Sakurai felt the Golden Sun series did not earned its place in Smash since the series received minimal content in Smash 4, with no sign of Isaac's AT and Dark Dawn becoming a big flop in 2010. I have doubted Isaac for the longest time because of those reasons, but he just might have a chance now, with that NeoGaf leak gaining a bit more credibility. I would like to see the leak become true because of Prince Sable, my most wanted getting in. But I do not wanna have false hope.
Personally, it is gonna take me a while to process the thought of Isaac having a chance at all. If he does appear, I would like to know why Sakurai decided to add him in the first place, beyond demand being the main factor.