If it was anything but fanfic, I'd agree with you that it's spoilerish. However... the great majority of people in fandom, I believe, want to read specific pairings. There are very, very few fanfic plots were there's a real suspence about what main pairing is (regardless of whether there's a happy ending for them), even in triangle configurations.
When it's the case people often tag it, for exemple, "Remus/?". I think that's a fair warning. It says : Remus is paired with someone I don't want to reveal for suspence reason, read at your own risk. But this is a rarity.

I wish there was a Character assassination warning too ^^