I'd love to be able to reliably generate a world with lots of little good and evil regions, such that a 4x4 embark can have good and evil plants and animals. The world should still have enough neutral regions to allow for humans and dwarves (obviously).
Reliably is going to be tricky, for the reasons that Fleeting Frames mentioned, but here's one that matches.
Whether or not this worldgen works again (without these seeds) depends on whether or not a medium sized not-good/not-evil human friendly area is created in the Northeast corner. That permits the human civ to spawn.
Remarkably, even though there's only 4 elves remaining, elves are neighbors at embark as well. Elves also appear to ignore savagery when settling a good biome, which was yet another learning step on this grand voyage of discovery.
I've provided three embarks, because they each have their pro's and con's. One has joyous wilds, terrifying and untamed wilds in a 3x3. One has pretty much all dead trees in the evil portion of the embark, sandwiched between two joyous wilds, while the last is pretty much half and half good/evil, with just a bit of dead ground/trees in the terrifying part.
The three embarks are steel friendly, but I skipped including prospects, as you didn't seem concerned about that. On one of these, I think the all dead trees one, three Ogre Corpses were spawned at embark time, and promptly wiped out my starting seven. So, beware!
Each of these embark locations has at least joyous wilds adjacent to terrifying.
And to re-iterate, if you don't care about non-dwarven races? This is trivially easy to do reliably.
worldgenCreated in DF v0.43.03.
[WORLD_GEN]
[TITLE:JCNORRIS00_1]
[SEED:1bsIl5ijVtyPeMhoZqYH]
[HISTORY_SEED:mrLogdriiiSK3sm5C32D]
[NAME_SEED:w6IPmVOA3kTwnUWsIbIJ]
[CREATURE_SEED:qmpeMHuUjZju0wHNWvp5]
[DIM:17:17]
[EMBARK_POINTS:2500]
[END_YEAR:1000]
[BEAST_END_YEAR:1000:-1]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:1]
[ELEVATION:100:400:0:0]
[RAINFALL:0:100:200:200]
[TEMPERATURE:0:100:3200:3200]
[DRAINAGE:0:100:200:200]
[VOLCANISM:0:0:0:0]
[SAVAGERY:0:100:0:0]
[ELEVATION_FREQUENCY:1:1:1:1:1:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[POLE:NONE]
[MINERAL_SCARCITY:500]
[MEGABEAST_CAP:0]
[SEMIMEGABEAST_CAP:0]
[TITAN_NUMBER:0]
[TITAN_ATTACK_TRIGGER:7:0:0]
[DEMON_NUMBER:0]
[NIGHT_TROLL_NUMBER:0]
[BOGEYMAN_NUMBER:0]
[VAMPIRE_NUMBER:0]
[WEREBEAST_NUMBER:8]
[SECRET_NUMBER:0]
[REGIONAL_INTERACTION_NUMBER:200]
[DISTURBANCE_INTERACTION_NUMBER:200]
[EVIL_CLOUD_NUMBER:200]
[EVIL_RAIN_NUMBER:1]
[GENERATE_DIVINE_MATERIALS:0]
[GOOD_SQ_COUNTS:100:0:0]
[EVIL_SQ_COUNTS:100:0:0]
[PEAK_NUMBER_MIN:0]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:0]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:0:0:0]
[REGION_COUNTS:MOUNTAINS:0:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:0:0:0]
[REGION_COUNTS:HILLS:0:0:0]
[EROSION_CYCLE_COUNT:1000]
[RIVER_MINS:0:0]
[PERIODICALLY_ERODE_EXTREMES:0]
[OROGRAPHIC_PRECIPITATION:0]
[SUBREGION_MAX:5000]
[CAVERN_LAYER_COUNT:1]
[CAVERN_LAYER_OPENNESS_MIN:100]
[CAVERN_LAYER_OPENNESS_MAX:100]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:0]
[CAVERN_LAYER_WATER_MIN:51]
[CAVERN_LAYER_WATER_MAX:52]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:10]
[LEVELS_ABOVE_LAYER_1:21]
[LEVELS_ABOVE_LAYER_2:2]
[LEVELS_ABOVE_LAYER_3:2]
[LEVELS_ABOVE_LAYER_4:2]
[LEVELS_ABOVE_LAYER_5:3]
[LEVELS_AT_BOTTOM:2]
[CAVE_MIN_SIZE:1]
[CAVE_MAX_SIZE:1]
[MOUNTAIN_CAVE_MIN:0]
[NON_MOUNTAIN_CAVE_MIN:0]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:9]
[TOTAL_CIV_POPULATION:1000]
[SITE_CAP:10]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:0:0:0]
[RAIN_RANGES:0:0:0]
[DRAINAGE_RANGES:0:0:0]
[SAVAGERY_RANGES:0:0:0]
[VOLCANISM_RANGES:0:0:0]
[PS_EL:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100]
[PS_EL:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100]
[PS_EL:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100]
[PS_EL:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100]
[PS_EL:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100]
[PS_EL:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100:100]
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[PS_EL:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400]
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[PS_EL:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400]
[PS_EL:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400]
[PS_EL:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400]
[PS_EL:100:100:100:100:100:100:100:100:100:100:100:400:400:400:400:400:400]
[PS_SV:100:100:100:100:100:100:100:100:100:100:100:100:100:100:0:0:0]
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embark location 1embark location 2embark location 3