I'm so confused. I read the translation of Kubo's PASH March interview (specifically about the rings), but then I also have read in a few places that she said the rings were symbols of Yuuri and Viktor being soul mates. Which is it?!
Sorry for the very late reply, I was waiting until I posted the Febri interview to reply to some questions since she mentioned the rings again.
I think the interview published in Febri might be the one where she explained more in detail how/why she had the idea to use rings. Apparently her intentions where to add something that would further deepen their relationship but at the same time make sense within the story (in this case as some kind of protective/lucky item for the tournament).
Also, this is the reason she chose to use the rings, but she didn’t talk too much in detail about what was going through the characters’ mind (though she did suggest that Yuuri didn’t mean it as a marriage proposal), therefore I guess fans can make their own theories for that.
(I’ve seen some people disappointed because the rings weren’t meant as an engagement, but they definitely still have a deep meaning, and also, even if they aren’t engaged, I don’t think that makes their feelings for each other any more shallow)