One thing I'm building into my new campaign world that I've never done before is the concept of technological progress. In the past all my worlds have had a kind of "locked in 1400" kind of mind-set. I'm planning on having things advance over the years.
As of the campaign's start date, smokepowder will have been invented 100 years ago, and I may advance the game a few decades if the game restarts at some point (or if I rebuild it for 4.0 whever it inevitably comes out), there may well be more elements.
Looking at the Gun Mage class from the IK site, I could see something like that popping up in my world, as an incredibly rare thing, then becoming more common over the course of 100 years or so... In 200 years, maybe steamships and dirigibles could make an appearance. I think magical/technological progress could make the whole world tie together really neatly.