We were wondering if the hint would be too obvious for a hint, then Papagenos talked about it during his stream and he was very close to not mentioning Touhou as it was mentioned last after dozens of other theories. So it really not that obvious as a hint.
Funny new addition to this theory, in today's tweet. Sakurai is affirming there is no hints in his tweets, it doesn't mean much because it could go both ways, it could be true, but it could also be something someone giving secrets hints should say and would say, especially the way he says it. Anyways, in that tweet he uses the word "toukou", which means "post". I think it's pretty funny, now I'm wondering if those Touhou-sounding words are really that common in japanese.