I've been reading the Malazan series by Steven Erikson and there is just a ton of stuff in it I'd love to see in a published campaign world. Fact is, Malazan is based on a D&D/Gurps campaign, so that probably really adds to this feeling.
Anyways, stuff I'd love:
1. Soletaken. Powerful shapechangers that are generally resistant to magic and many of whom are mages. Some of them are dragons, others turn into a horde of rats. All of them are vicious, nasty bastards.
2. Warrens. Magic is aspected to warrens. Many mages can only access one warren, though cases certainly exist where mages can use a bunch of different ones (Quick Ben and Bottle being the primary examples).
3. Ancient races that are still around, though very rare and generally extremely powerful. Examples include the Toblakai, the Jaghut, and the Tiste variants. This would also work fine with elves if they were not just the tree-hugging recluses most settings use that mid-level adventurers can kill without a ton of effort.
4. A real live Empire that includes multiple cultures and is generally quite effective at accomplishing it's goals. Most settings either have the empires long vanished or generally collapsing (Forgotten Realms is a prime example).
Van Richten's Guide to Fiends
6 hours ago