It appears like it was to be plot-centric, with zones specific to an era.
This would make it dissimilar to Sonic CD.
These zones were divided across four eras:
Present, Ancient Past, Altered Present, and Future.
Naturally, the game would start in the Present.
The Past would follow, then returning to an altered Present.
Lastly, the game would conclude in the Future.
Each zone in the Present has variants across eras.
Green Hill/Emerald Hill pairings:
Hill Top in the past
Dust Hill in the altered present
Chemical Plant possibly in the future
Ocean Wind pairings:
Oil Ocean in the altered present
Blue Lake potentially in the past
Chemical Plant in the future
Woods Zone pairings:
Casino Night in the future
Sand Shower pairings:
Rock World in the past
Rock World in the altered present
Genocide City 2 in the future
Metropolis Zone pairings:
Tropical Sun in the past
Genocide City 1 in the future
For reference here's the past map:
Blue Lake is likely in the area of Olympus,
which could mean it turned into Aquatic Ruin.
It could very well span the water and forest.
Blue Lake could also be a past for Woods Zone.
Rock World Zone could have become Hidden Palace.
It is unclear if the zone is represented by the forest, or by the pyramid.
The badniks of Hidden Palace point to its placement in the past.
Tropical Sun could be related to Metropolis.
Shellcracker, badnik of Metropolis, fits the likely beach theme.
Asteron, another badnik of Metropolis, would fit a beach theme.
The Snail badnik could have fit too.
Hill Top is undoubtedly related to Emerald Hill.
For reference here's the altered present map:
Dust Hill is in the same location as Emerald Hill.
Dust Hill shares a level slot with Mystic Cave, inspiring the badnik selection.
Dust Hill is likely to be an unseen zone however.
Perhaps a zone that was burned down.
Oil Ocean definitely overlaps with Ocean Wind.
It could also be a portion of the site where Chemical Plant was built.
Blue Lake could be a past version of the region.
Rock World Zone possibly spans from the rocks to the pyramid.
It could very well be Mystic Cave.
Rock World is connected to Rock World of the past, and Sandy Shower.
Banper goes to either Rock World past or here, along with Sandy Shower.
For reference, here is the Future map uncolored:
The Death Egg is notably mechanized, and follows Genocide 2.
Chemical Plant overlaps with Emerald Hill and Ocean Wind.
Casino Night overlaps with Woods Zone.
Genocide City 1, or Cyber City, overlaps with Metropolis.
It could secondarily overlap with some of Sandy Shower's area as well.
Genocite City 2 appears to cover Sandy Shower/Rock World.
Interestingly, with the zones grouped like this there are only 5 areas*
*(Well, there are 6 including the presumed Death Egg.)
