Greyhawk is full of contradiction when it comes to the functionality of technology in the setting. For example, black powder isn't supposed to work unless you're a deity like Murlynd, or if you're a paladin of Murlynd then you get an exception too. But in general it's an unwritten rule (for DM's personal preference) that anachronistic technology isn't supposed to work on Oerth. Until it does.
Crashed spaceships in the Barrier Peaks yield ray guns and robots. A City of the Gods and frozen automatons lay at the fringes of the Land of Black Ice. Futuristic sailing ships are caught in a tropical sargasso. Ancient artifact level machines and mechas stay hidden until found by adventurers. Gates to alternate Earths can be found that work both ways. I'm sure if Greyhawk had enjoyed an unbroken line of development from the 80's to present we'd have even more instances by now. The point is a variety of genre-mixing technology is there if a DM knows where to find it or if they want to keep it out of their medieval fantasy then no one is the wiser.
What if we ignore the Epoch of Magic and apply all the above examples as overt changes to the setting? Put another way, what if tech and magic mingled freely in Greyhawk? Perhaps an Epoch of Magi-tech. Well we might end up with a world more like Eberron I'd assume. Automaton/Robot "warforged" would become a viable PC race. Larger magitech monsters and vehicles would become more common blurring the line of science and necromancy. I'm imagining Final Fantasy type flying ships, larger golem-like machines leading sieges. Black powder weapons of course would lead to an explosion of crafting and alchemist class characters. None of these advances precludes magic users either, it only enhances them.
Deities would need a slight make over as well:
Murlynd would be the prototypical hero-god of magitech; the bar by which all adventurers are measured.
Boccob, Delleb and Zagyg certainly jump into the weird magic-tech mashup with even more futuristic arcane objects.
Hextor (and perhaps others like Heironeous) as god of war would lead in cutting edge machines of war both on land and at sea.
Moradin, Fotubo and their like would not be outdone in the crafting department though.
Gods like Xerbo, Zilchus and Bralm would encourage and profit off the tech's spread to common folk.
Stranger deities like Celestian, Tsolorandril and the entire Olman pantheon would also focus eyes to the stars way more than they do currently.
And I don't even want to think about Tharizdun paired with technology!
So yes, magic and tech in Greyhawk can make for an exciting fantasy world. It's all a matter of how far do you take it?
