I tried out the new world generation today, and found some rather peculiar sights, specifically regarding the Plains biome. From my experience, they appear to be way too hilly. (see attachment plains.png)

I tested other flat biomes such as Snowy Plains and Sunflower Plains, but these seem to be unaffected. Although I did find some hilly areas in these biomes as well, but these seemed to be the exception, rather than the rule. (see attachments)