THIS IS AN IMPORTANT NOTICE
The source is Motokura and all he said was
>"I can't give you very precise details, I can tell you that we started developing it after finishing Super Mario Odyssey,".
This is not confirmation of 8 years, this only means it went into development after Odyssey was complete. It also doesn't mean that they entered active development immediately after Odyssey either.
THIS IS AN IMPORTANT NOTICE

I fucking hate this place