Well since the average campaign lasts under a year, I would come out with a new campaign boxed set every year. There would be aventure support for that year and then a new campaign setting would be released. Sometimes I would use an older setting, for example Dark Sun. I would start it back at the beginning of the timeline, rather than start where it left off or try to update it.
I would release those DM books that MerricB came up with. I would do the "lenses" idea too. I would definently release a bunch of stuff for making low magic settings work in D&D. There is zero support for that in the core rules. I'd probably release d20 Fantasy, which would be based on the d20 Modern rules, but set in D&D worlds. Then I would merge the two in 4e.
I would release those DM books that MerricB came up with. I would do the "lenses" idea too. I would definently release a bunch of stuff for making low magic settings work in D&D. There is zero support for that in the core rules. I'd probably release d20 Fantasy, which would be based on the d20 Modern rules, but set in D&D worlds. Then I would merge the two in 4e.