I remember hearing from one source or another that this book is supposedly penned by Vecna. How amazing would it be if the book was really more of a journal of sorts, a tour of Vecna's rise to godhood, personal narrative not unlike Iggwilv in the Demonomicon but a little more elaborate, taking us through his story, stopping points along the way detailing crunch. It begins with his lowliest days and giving guides/inspirations/crunch/flavor for Heroic! There is so much just in that alone: the morality of the material world, how magic can be evil, the warlock debate, being an evil character amidst good PCs, then specific places/items/powers Vecna visited and the villains he met, bested, or was burned by on his way to powerful wizard.
THEN we hit Paragon, when Vecna has become a powerful wizard in search of lichdom, and we visit all the villains/locales etc etc he encountered to get there, in detail, crunch wise touching more on communion with planar entities, the process of becoming a lich, attracting followers of evil bent, influencing more powerful people.
THEN Epic, where Vecna is a lich looking for godhood, and all the planar sites he visits, all the artifacts he steals/destroys, the villainous archdevils/demons/fey/dragons he bests or tricks or makes accords with, and talks about the dark and selfish road to godhood for PCs, the establishment of personal cults and religions, rituals for taking the souls of powerful slain foes, creation of evil artifacts, and so on.
Yeah, a totally amazing framework like that would sell me in an instant. It's really the best of both worlds. On the one hand, you're appealing to the older editions via the Vecna framework, but you're also giving us something new in the specific journey he took from wizard to god, and with 4e crunch to support it.