I... wouldn't *dodges rain of rotten vegetables*
I loved the setting. I loved the tone. I just don't think, given a newer and seemingly more adventurer friendly cosmology that we need it. I would (and I already recognize this as a likely unpopular idea) do a single book called "Planecape" or something similar. It would detail the core gods, and maybe a brief extended pantheon, but not focus on them. It would provide information on the various planes, how to get to them, how to survive them, and what you will find while your visiting. Factions, as groups of mortals who inhabit the planes, could be covered. Sigil could, possible, be reimagined and provided in some detail. I see it as a city of gateways floating in the abyss. Doorways to everything, surrounded by nothing. All levels of play would be covered, but high levels would be emphasized.
A lot of detail could be provided about how characters with 21+ levels interact with higher powers and where characters end up post-30. Or, if there is a ton of extra room, the planes could be treated as an expansion. With 10 additional levels of hot god on god action.
It would be a Deities and Demigods, Manual of the Planes, Immortals Handbook compilation, all provided with as much planescape flavor as can reasonably be packed in.