So, in my head, I have a somewhat different view of Lex's sainted mother. This rises mainly from the Alexander the Great series written by Mary Renault, and how I think Lillian could have been like Olympias, Alexander's mother.
For those of you who have no idea what I talking about, Olympias is a, er, powerhungry harpy. She marries Philip of Macedonia for power, bears his son, and spends the rest of her days manipulating Alexander into hating his father. She wants her son to be even greater than Philip and will stop at nothing to help him attain this greatness.
I think there's support for this in canon too. I mean, take the watch Lillian gives to Lex on her deathbed and the story that goes along with it. She's clearly just as bad as Lionel about the obscure historical references and the "greatness is a rarified air one must be taught to breathe" thing. She's telling her son to be like Napolean.
I was looking at the quote this community has on its userpage and it can even be read as being manipulative. Assuming Lex repeats her story somewhat verbatim, she basically tells her son that, after she dies, the only way she will ever be with him again is "through the power of his greatness." I mean, that's almost like blackmailing him to not be mediocre.
And I can't see Lionel being that interested in anyone who didn't present a challenge to him. Something to conquer, so to speak. A shrewd, intelligent, but ruthless woman a lot like Olympias would have been a perfect match for Lionel.
Also: you cast Gillian Anderson as Lillian! Squee! That is so perfect.