I liked the boxed sets FR did in 2e days with regions of the world. They had softcover books of 32-64 pages. I think one was the regional overview and another was for an adventure in that land. They could throw in some maps and encounter maps.
What I am wondering is the cost of printing. I remember reading that this part is an incredible amount of final cost. The boxed set book were just folded and stapled. The heavy paper and binding is nice, but cheaper would be better to me. I mean, when 6e comes out in a few years most of the 5e stuff will be very limited in use.
6e is a lot more then a few years away. It's still growing at huge rate and it will most likely continue to do so for at least two years, it would be even more years before sales dropped enough to warrant 6e. And honestly if there is a hit D&D movie in the next few years, it will cause D&D to explode further boasting the market, and adding possibly another decade to 5e's life span.