My idea for a 4th homeworld is Spring Savanna. The level would be very open with some trees and include Hunters house since cheetas are from the savannas (based on African Savannas). The levels in this homeworld would not be based on its similarity to the enviroment but based on exotic travel destinations. The levels would be Pyramid Scheme (based on Giza Pyramids), Mountain Madness (based on Mt. Everest), Tropical Trouble (based on a Pacific island), Easter's Here! (based on Easter Island), Grease (based on Greece), Bi-Polar (based on north and south pole. Also would let you travel to both.) and Rainforest Speedway (based on South American rainforests).

I quite like this but I believe Spring Meadow would have also been a nice setting.

Well technically Sunny Beach is the 4th home world...

You mean Dragon Shores?

Sunrise Spring was supposed to cat as the extra spring level. I always thought Idol Springs was though lol.
Anyway, Ill try make one, sounds like a fun idea.

Huh, that's interesting. Never knew that.

Summer FOREST
Autumn PLAINS
Winter TUNDRA

I would say it would be called Spring Ocean. It would be similar as Evening Lake in Spyro 3.  As for levels, I would say it would become the second homeworld (guess). The levels as for Summer Forest as described as Beach, lakes, hills, and rain storms (hurricanes).  In Autumn Plains, the grass yellower (Zephyr), getting colder (Crystal Glacier), Deserts (Shady Oasis and Scorch), and Winter Tundra you have, cities, marshes, palaces, and farms are what you don't expect in Winter. So in Spring Ocean, I would expect swamps (Frog Zaire), a level with giant mosquito since that's when mosquitoes start to spawn (Neirce Pier), and a level with unpredictable weather with a a guy with a Hawaiian hat on (Windy Palace), and one last level, a level in total darkness, or in twilight, where a giant firefly talking to you (Dark Valley).  Hey, this is all made-up by me.