Personally I don't think 5E should produce any splatbooks in the traditional sense. However, given that WotC still need to release books to make money, what I think they should so is cross-pollenate EVERY book with an adventure or adventures
. So, for instance lets say we release a book about...
- New Assassin Class...tie that in to something like the Assassin's Knot adventure.
- Running a Stronghold...tie that into a Keep on the Borderlands style adventure.
- Adding Sci-fi Elements...tie that into an Expedition to the Barrier Peaks.
- Wilderness Survival Guide...something like Isle of Dread
- Book of Traps...tie that into a Tomb of Horrors trap-fest
- New 'Themed' Monster Book...dungeon delves adventure anthology.
- New Planar book...Dead Gods (Astral), Temple of Elemental Evil (Elemental)
- Book of Magic Items...find them at White Plume Mountain
Just for the record I am not necessarily advocating the re-release (or in many cases re-re-re-release) of old adventures, I am just using the above as examples. There is no reason why the adventures couldn't be wholly new.
The benefits of this method are:
1. More Adventures:
Adventures were much neglected by WotC because they apparently don't sell well enough. By tying the adventure portion to specific design mechanics they could give them a new lease of life.
2. Show Don't Tell:
In the adventure format, the designers can show exactly how assassin's operate or how to best set up traps. Its like a step-by-step DIY guide.
3. Fluff + Crunch:
Any adventure needs to tell a story and thus strikes a healthy balance between fluff and crunch.
The marriage of adventure + mechanics could see a return to the inspired adventure design of the past. Instead of 'just another dungeon', each adventure would literally add something new to the game.
5. New Approach:
How many Manuals of the Planes, Draconomicons and Complete Fighters do they expect us to buy. I'm a bit worn out by the 'same old same old'. Try something new.