Ok, I have a theory, it's not really a "new" theory , and i have a feeling that not many people will agree. But my theory is that the main characters (5 of them) from the WMPP era were in love with Lily.
DUH.. she was his wife.
I think that Remus and Lily are very similar, even though Lily is popular, she is smart and logical. I think that Remus and her were probably friends long before James came along, and there would have been some romance, even if it was one sided on Remus's part. I think that the reason we saw none of this is that.
a. he didn't believe he deserved her. We see that with Tonks now, he doesn't think they are right for each other.
b. went James started to like her, well she was off-limits. Perhaps Remus started to like/love was after James, and Remus was loyal to his friends, and would have kept it to himself.
Lily is a strong, person a confident fighter. Peter admires these qualities, and I think he would have near-worshipped her. Peters reasons for liking Lily are easily, as she was popular and smart, and desired. Why would we have not seen this, well i think that Peter would have perhaps confront Lily with his Love for her, but she would had (of course) shot him down. I think they may have lead to his betrayed, when James and Lily are finally together
The Last of the unfamous four. He probably like Lily for similiar reasons to James, him being a similiar character. But he is (was, past tense.. he's dead... cry) Loyal to James. If he did have feelings for Lily romantically, then, he would have told James, he's best friend first, and James, being the leader would have come out on top. But.. i am not entirely sure that Sirius had romance feelings for Lily, but he did Love her. He is Harry's Godfather, and would have been great friends of bothe James and Lily, so I think his Love would be in a more Friendly way.
My favourite one. I think he did Love Lily, definatly. But first let me explain what I think Serveus was at Hogwarts. He was a Slytherin, and was attracted to Power. And he "click" (yes, i am a girl, i used click), was with people of power who became deatheaters. Snape went with the flow and also became one. Now Lily, Lily was strong and confindent, and I think that Serveus would have liked her because she was everything he couldn't be. She had a "power" of her own, and she didn't go with the flow, she was her own person. I think that Serveus wanted to be a person like that, but couldn't and I believe he carried a secret Love for her through his years at Hogwarts. I will used something I sometime used to decribe what I think of Hermione and Draco, If they had met and exist in another world, they would have been able to be friends, but in that world they could not have.
This is my theory, and many people will dismiss it, thinking it is far-fetched, and not supported at all by the books. But I believe the Popularity of Lily did attract these admires, and will influence the Plot. I at the moment did not include any references, but this is (in some distant way) based on the canon plot.