I like the idea too, I've read a few threads discussing different breeds of domestic creatures, so this would fit in well with that. Perhaps there could possibly be a way to have predefined certain special species and define sets of different characteristics that can be mixed and matched? For example, see this mockup:
[CREATURE:WOLF]
[SIZE:5][SIZE:4][SIZE:6]
[COLOR:BROWN][COLOR:GREY][COLOR:WHITE]
[MARKINGS:BROWN][MARKINGS:GREY][MARKINGS:WHITE]
[MARKGLOSS:STRIPES][MARKGLOSS:SPOTS]
[BODY: ... WOLF_TEETH:TAIL][BODY: ... WICKED_TEETH]
[BIOME:TUNDRA]
[BIOME:FOREST_TAIGA]
[BIOME:ANY_TEMPERATE_FOREST]
[BIOME:SHRUBLAND_TEMPERATE]
That would give us different species all living in biomes wolves would normally be found in. Different species could be standard size, pygmy or large, they could be brown, grey or white with markings of similar coloration. They could have stripes, or spots. They could come in vanilla variety or be tailless and have needle-like teeth. If you wanted to define your own species, you could do something like this:
[CREATURE:WOLF]
...
[SPECIES:DIRE]
[EVIL]
[SIZE:7]
[COLOR:DUST]
[MARKINGS:BLACK]
[MARKGLOSS:PATCHES]
[BODY: ... ]
[BIOME:ANY_DESERT]
...And you would have a specific species of very large dust-colored wolves with black patches living in evil deserts. You could also define several sets for specific biomes, so you could have several varieties of white wolf in a tundra biome, for instance, or several kinds of pygmy wolf in a good biome. Or something.