I'm not sure but I think it would be cool if N/S or even better, elevation would be the driver of biomes. One REALLY COOL thing about Arizona, US is the diversity of biomes. This diversity is driven almost completely by elevation.
Which leads to a pretty cool diversity in the state due to the huge elevation differences
The biomes of Arizona, USA: 1 = Alpine Tundra, 2 = Spruce Alpine Forest, 3 = Petran Montane Conifer Forest, 4 = Juniper-Pinyon Woodlands, 5 = Interior Chapparal, 6 = Plains Grassland, 7 = Desert Grassland, 8 = Great Basin Desertscrub, 9 = Mohave Desertscrub, 10 = Chihuahuan Desertscrub, 11 = Encinal and Mexican Oak-Pine Woodland, 12 = Lower Colorado River Sonora Desertscrub, 13 = Arizona Upland Sonora Desertscrub
I think completely replicating all of these biomes is a stretch but taking the current 7-days biomes and applying them based on the elevations of the random gen maps would be a really cool feature and allow the player to have a decent idea of "how do I get to X biome?" as much as a normal person would if dropped in the world somewhere. Up is going to be colder, down is going to be warmer (in a climate sense).