Nearly since Shards of Alara block came out, Magic rumormongers and custom card creators have been imagining what the allied-color triples in that particular multicolor-themed block would be like if they were enemy-color wedges instead. Questions about it on Mark Rosewater's Tumblr blog became so prevalent that this theoretical world got its own nickname: BizarrAlara, a riff on DC Comics' Bizarro, the flawed Superman clone whose verbal tics are infamous ("Me am not Bizarro! Superman am Bizarro friend!"). Many custom designers have taken it upon themselves to make this BizarrAlara a reality (including a few of MTGSalvation's finest), and whether by mutual influencing of each other or by convergent creation, their visions for the wedge demiplanes overlap scarily often. If they're any predictor, here's how a wedge version of Alara would look:
White-black-red: This is almost always the same thing - a bleak Norse-themed world of endless war where the fallen are resurrected to fight and die again, presided over by Valkyrie tyrants who believe might and right are the same thing. The exact name Valheim has even been used multiple times for this. Oft-used themes include attrition, Auras and Equipment, and attacking with lots of creatures. Expect mass removal as well. The keyword even tends to be "This spell costs 1 less to cast for each creature that attacked this turn" and variants thereof.
Blue-red-green: The one very consistent thing about this wedge is the flavor. Usually this is a tropical paradise of abundant mana, often explicitly using names inspired by Hawaiian mythology. Mechanical themes often include drawing cards and casting multiple spells in a row, as well as mana ramp. Elemental tribal themes are also popular among people who imagine this wedge.
Black-green-white: This wedge is almost as oft-repeated as the white-centered one. The flavor is almost always Ancient Egypt or Mesopotamia. The mechanic is almost always recursion based. This is the slow, midrangey, reanimator wedge where everything is immortal and stagnant - exactly like Grixis without all the horrible disorder. Unsurprisingly it's still as unpleasant to live in as that shard was.
Red-white-blue: This one has much more originality between designers than the others do, simply because it's so hard to figure out what the mechanical commonalities even are. The phrase "world of artists" comes up a lot, and artifacts and/or enchantments matter usually plays a role. There are ice palaces and bards, possibly rich Arabian Nights-esque mirage deserts with splendid pleasure domes ruled by Djinn, and a whole lot of hand-wringing (justified, mind you) about how red's emotions can be love and happiness and not just anger.
Green-blue-black: Imagine the reason The Mimeoplasm has a dinosaur arm. This tends to be a primordial soup bayou of ruthless survival of the fittest. Themes often include having the biggest creature, having the most abilities on your creatures, and having the highest hand size. Because you should try to grow a brain as fast as you can when scornful mutated overlords regard their evolutionary lessers as just food.