The attitude I have personally employed in regards to pictures tweeted by Sakurai is that the man enjoys making fun little jokes and memes with his particular sense of humor, and that he would never actually intentionally drop a hint or a wink towards whatever's coming down the pipeline. Considering that he himself has been on the record saying he actively turns down invites to some events and interviews because people will just start yelling about what it means for Smash, I highly doubt that he'd be willing to do that to himself with his own twitter account and dev pictures.
Sometimes, people just like to make fun jokes and references, especially if it is in relation to things that they like.
And, yes, before I forget; His little hand gesture for the Byleth reveal was certainly in relation to Three Houses, but considering that even with that knowledge, it still was only because he was counting in Binary, nothing anybody would have predicted on its own, and it was because he was counting the total games for Fire Emblem, not because the three fingers meant Three Houses -- I'd say that this, alone, is the closest we get to Sakurai hinting at anything, and even then, it was a very particular, very obscure thing he was doing to get to that conclusion to begin with.
It's healthier to just take the pictures he posts at face-value unless he outright states one day, "Ah, and this picture, I wonder what it means...?"