I don't feel like Sakurai has hinted Skull Kid in the slightest, at least not in a direct manner, a lot of it is assumptions made by fans. I think the one solid thing he has in his favor is that his AT looks to have been replaced by The Moon, but all of the other stuff with Skull Kid figurines and colored chairs are just theories, you can't blame Sakurai if those don't pan out. Also, take it from a Ridley fan, don't ever ever ever assume a character is in just because "Nintendo wouldn't do that", we went with that slogan for over a year and were burned at the end of it.
I of course hope for Skull Kid myself, but I'm taking all of these so-called hints with a grain of salt. I personally think The Moon AT is encouraging for him, just like I think the Knuckles AT is encouraging for Shadow's chances, but I'm not at that stage yet where I feel like he's a lock, just that he's got a good chance. It's best to be cautious in these situations.