Make an Inner Planes Campaign Generator: this would be a single, probably large volume. It would have a single set of hex maps and a large number of tables, a bit like my approach in Yoon-Suin with individual DMs populating their own maps, but the tables would be re-skinnable by plane. So you would roll a dice and consult a certain table, and the result would be abstract enough (e.g. "undead spirit of an ancient sorcerer who has imbued his soul into an elemental whose consciousness he has enslaved"; "Trading outpost populated by dwarves and protected from the elements by runic magic"; etc.) that it could mean something similar but different depending on whether it was in the Plane of Water or the Quasi-Elemental Plane of Salt or the Para-Elemental Plane of Ooze or whatever. Alternatively I would be tempted to make a setting book for every single inner plane, but that may be beyond even this pipe dream.
Make a proper version of Changeling: the Lost: White Wolf had some good ideas, but their games are all very precious and focused on teenage concerns: existential angst, feelings of alienation and difference, emotional highs and lows, etc. While in a sense this is part of their genius, in that they managed to bottle something that a certain portion of teenage nerds would respond to very strongly, it also often results in a very weak and amorphous sense of what is supposed to be going on beyond a group of people being sad they are vampires/angry they are werewolves/glum they are dead/ennuye they are fairies, etc. Changeling: The Lost is the classic example of this: the PCs are human beings who were kidnapped by faeries and taken as slaves, but who have now returned or escaped....which could make for a great urban fantasy sandbox affair if only the makers of White Wolf hadn't wanted the whole thing to be some sort of worthy meditation on victimhood and how unfair life is. The whole thing is ripe with interest: you've been enslaved by faeries for God knows how long, you have been replaced by a Fetch who looks like a bunch of twigs in human form but everybody else mistakes for you, you have this understanding that there is a supernatural other world out there, you know of a group of other people in the same position: now what? Forget all the sitting around whining about it and coming to terms with it.
Make In a Jamesian Age: a story game using the In a Wicked Age rules and based on the works of MR James. Each time the PCs are antiquarians or academics investigating some mysterious church, country manor, library, or whatever, and the oracles contain things like "an ancient Anglo-Saxon crown", "a version of the testament of Solomon written on human skin", "a deep dark well", "a gnostic sorcerer" and so forth. Full of Satan worship, the Apocrypha, ghosts and devils, and mysteries left completely unexplained: forget all that Sword & Sorcery nonsense; this is Ghosts & Scholars.