Kthulhu wrote:
 My preference would be similar, but not exactly the same.  One big book that collects the best of ALL the previously released material for a setting.  Perhaps not in as much detail as prior focused supplements, but enough so that it could be considered the definative, fairly comprehensive, go-to source for information about the setting, regardless of what edition you play. 
I would be beyond ecstatic if this happened. Although, I'm sure it won't... That's not the best way to make money, unfortunately.
I am crossing my fingers for a 5E Planescape though if this doesn't happen!