What else needs to be done, though? What areas are left unexplored? Where are the new frontiers for this corner of the hobby? Well, in my view they are:
- Innovations in overland travel. I think Veins of the Earth, when it eventually comes out, will do this for the underworld. And a lot has been written about dungeons. But it seems to me that "the PCs travel across the Dragon Mountains from point A to point B" is the kind of episode whose surface has barely been scratched. Making overland travel interesting is an area I want to see start to be really properly mined for ideas.
- Underwater adventures. The first person to make a really good underwater module, campaign setting, etc., wins a coconut.
- Exploration generally. There's a region of a campaign setting's map which is unexplored. The PCs set out to find out what's there. Currently what are the options apart from making it a hexcrawl with some random encounters and monster lairs thrown in?
- Usable systematic ways to make dungeons (or hexmaps or anything else) evolve over time with or without the influence of the PCs. I want to see ways to make a dungeon in particular change dynamically over time, so that the DM can roll a few dice in between visits by the PCs and find out what the inhabitants get up to in the interrim.
- Alchemy. Not just blowing stuff up.
- New real-world cultural inspiration from untapped mythologies and regions. Where's the Aztec-inspired campaign setting? The Maori-inspired one? The Ethiopian-inspired one? Etc.