I don't know about the rest of the RPG community, but I've come to use the term "Haywire" whenever I go way outside the canon of some setting, and often mix it up with other settings, other games and sometimes even other genres. It is when consistency and believability take a back seat to crazy ideas which may turn out to be silly, or might end up being really cool.
One of my first haywire settings was the Forgotten Realms. This was back in the days of AD&D, and although I certainly liked a lot of the setting (I still do), changes made by TSR at the time (including the Time of Troubles) made me veer away from the official canon. At the same time I had accumulated a lot of gaming material such as the dark red 2nd Ed player's "complete" books, a lot of Dragon Magazines. Thus I decided to use all the strange and cool stuff without worrying too much about what other people would think, or if it would be taken seriously. This was before the days of the Web, and I knew it wouldn't be published. I called the project "Forgotten Realms goes Haywire".
These ideas for Kaelaross going haywire will not be carried forward in this blog, this is just a diversion. Nonetheless, some of the ideas I've had include:
Combining the Mystaran concept of the Hollow World with MAR Barker's Tekumel (Empire of the Petal Throne). If you go down deep enough into the Underworld, you emerge into this bizarre, alien world, where even the plants and animals are foreign. Mighty Empires clash, and political intrigue abounds. The Tekumel gods of Change and Stability are in fact different aspects of the Kaelaross gods of Law and Chaos.
Taking Warhammer ideas about chaos and running ragged with them. Chaos warriors (actually the inspiration for the Traitor Legion), chaos mutation, chaos sorcerers being granted new, vicious spells and many new beasts of Chaos including Chaos Centaurs (who inspired the Winter Centaurs of the Twilight Forest)
An all-human land-mass, possibly Bursia, where characters from non-Tolkien Swords and Sorcery can be found. There are no demihumans found there, and non-humans are viewed with anything from wary suspicion to outright hostility. Here can be found the grand cities of Lankhmar (Fritz Lieber) and Sanctuary (Robert Asprin's Thieves World). Quite a few ideas and characters from RE Howard's Hyboria can also be found here.
(Update - This has now been partially implemented in that Bursia is considered entirely human).
There are mixed-race city-states as well - in what was Bellenos there are now cities that have survived the terrible Summoning, including the City State of the Invincible Overlord, which is across the sea from its rival, the City of the Spire, Ptolus.
Michael Moorcock's Melnibone has fascinated me since I read the Elric series of books. His ideas about Law and Chaos as cosmic forces shaped both early D&D and also Warhammer, and my own ideas about fantasy both directly and indirectly. Maybe the Melniboneans were the near-human aristocracy who ran the Empire of Telthus.
Although there is a map of the west half of Toutus, I have not decided on what the eastern half looks like. Perhaps it looks like the Flanaess (a.k.a. the World of Greyhawk), or maybe the north-east of Toutus includes the land of Blackmoor (Dave Arneson's version, rather than Gary Gygax's), with a rump of the collapsed Toutatian Empire taking the place of the Thonians.
In terms of new rules, anything that is vaguely Swords & Sorcery or High Fantasy is fair game. This would be an ideal opportunity to use all those ideas from Dave Hargreave's Arduin supplements (some of which are completely mad, but that's what going Haywire's about!). Grab and use anything you like the look of. Articles from Dragon Magazine, supplements for other games, even things you've seen on computer games. You want to include the Witch Doctor from Diablo 3 as a character class? Fighting against Quillboars from WoW? And the big bad guy is the Warlock of Firetop Mountain ? Excellent!
Don't forget the Web. As well as the online bookstores, there's a huge amount of free stuff out there, and I'm sure a lot of the bloggers would be pleased to hear their ideas have been used.
My one caveat is this - you may want to keep haywire campaigns separate from your more serious campaigns. Why not roll up some new characters? Take the opportunity to try out some new classes, races or abilities. You like the idea of 3E D&D feats? Go haywire with them. This means if people do get tired of the haywire campaign (it gets too outlandish/silly/overpowered/fanboyish) then the more normal, consistent campaign is not damaged or adversely affected.