No. That is a false rumor.
In fact, they have improved the biomes in a number of ways for their next update. The forest biome has more varied areas of open areas and densely packed clumps of trees and underbrush. They changed the look of trees in the wasteland. Each biome will have an environmental hazard that will slowly kill you until you attain the needed upgrade kit to be able to deal with it. There will also be new biome specific special infected coming. So biomes are definitely not going away.
Navezgane is getting updated specifically with the biomes in mind. It is not being changed to just one biome. The positions of the traders are being shifted to make them better.
Seasonal shifts in nature and weather are not planned at all for this game.