Recently Insomniac Games stated in their livestream on Spyro 2: Ripto's Rage! that there was never a scrapped fourth homeworld based on Spring. It was all a fan theory.
https://clips.twitch.tv/SavageShyWolfWTRuck
Game designer Michael John soon revealed that a Spyro homeworld was planned but in the end was merged with Summer Forest, the first home world in Spyro 2.
https://twitter.com/MichaelMJJohn/status/1235767802184839168?s=20