I think Moore would have a big problem suing because so much of his "original" work is based on their existing characters. Even "Watchmen" started as his spin on the Charleton characters.

For example:

Do you compensate Alan Moore for "creating" Rorshach when he bascially was a renamed version of the Question? And when you do, what about Ditko's rights? Do you have to credit Ditko as a co-creator of Rorshach? I can't see Moore going for that.

And if taking an existing character and putting a new spin on it (ala, again the Question) entitles one to compensation as the creator what about characters who were revised and revamped but kept the same name? Is, for example, Frank Miller now entitled to be considered a co-creator of Batman because of how radically he re-envisioned aspects of the character?

It really is more of a minefield than Kirby supporters like to believe. And, as I've said before, Jack Kirby was a well-established pro when he worked for Marvel in the 1960s and knew exactly how work for hire operated. He got paid the same whether a book sold well or it flopped. He certainly didn't hand his paycheck back in when a book didn't sell. He gambled that signing off his rights was a better bet than keeping the rights and self-publishing.