There's a pretty crazy theory circulating around that the Yasuo in the League is Yone. The basis of the theory goes like this. -Yasuo refuses to kill Yone. -Yone, still believing Yasuo killed the elder and this would redirect the attention of his family back to him, kills Yasuo. -Yone finds out Yasuo was innocent. -Yone, crazy with the grief of killing his innocent brother, takes on Yasuo's identity to 'keep him alive'. The reasoning for this theory coming around is due to the PROJECT teaser. Number one and number four having the same number, corrupted memories, et cetera. Some people also picked apart some of Yasuo's quotes, and some noted some of them don't even fit Yasuo's role.
The theory is, naturally, completely outlandish and is to be taken completely with a grain of salt. I enjoyed reading it. A flaw off the top of my head would be how did Yone learn wind techniques, but now that I think about it, Riven has a wind technique completely unrelated to Yasuo, so maybe it's people that Yone learned a different wind technique, as Yasuo was stronger.