Ok, so WW stabs Soraka, and gets blood on his knife... but that's not enough for the potion. Seems a bit sketch to me, but I can accept that.
What I can't really accept is that this new story adds tension between WW and Soraka. I know that PvP battles aren't exactly considered canon but... as someone else mentioned, these two see each other on the fields of justice all the time. Heck, WW ganking Soraka bot lane happens very often. If the two run into each other, WW is going to kill her (unless he is controlled by an unskilled summoner). This, in my opinion, completely removes any tension this story is supposed to give to the two characters, because their meeting is completely inevitable, and the outcome very obvious. I found it much more interesting before where WW has a love-hate relationship with Soraka, because she cursed him with a monsterous form, but he loves being a monster. The fact that the spell used to transform him into a monster cost Soraka her deity not only makes WW seem more bad-ass (so strong and dangerous she was willing to become mortal to curse him), but also adds characterization and depth to Soraka's character. That's ongoing tension, because we don't know where it'll lead exactly.
This story is pretty childish in complexity. WW wants to kill Soraka, or he loses his mind. Ok... so when WW kills Soraka in a game, why don't we see anything happen? What changes? Further, if he fails to kill Soraka... what would change? Wouldn't he still be a feral monster? Why should I care? How does that change WW or the LoL universe at large?
It also seems to me that Soraka doesn't really have any business to deal with when she meets WW. Yeah, he betrayed her... but what does she have to gain by fighting him, on a personal level? She doesn't seem the vengeful type to me, so that's out. She isn't motivated by money, or power. So what's left? Really all that's left is the "Defending my friends!" angle... which is fine, but you don't get any deep characterization going that route, which seems to be the point of this retcon.
So I have to ask... how do these story changes make WW and Soraka better, or at least more interesting, characters?