True but what we definitely know was that the Golf Course is intended for the game but didn't quite make the cut for the final version. Why would it be there on the map in the first place? Definitely not for looks. haha.
I'm going to stick with the late-development cycle part since it makes a bit more sense to me that they were trying to make 8 trial areas similar to the 8 gym leaders in other regions. Just speculation though.
For the areas not being expanded, it's only a minor thing but I was expecting a bigger structure inside hotels, story buildings, the power plant (I honestly thought that you could go to the back of it), the missing plots of land, the golf course and that lake area where there's water streaming from the rocks (I'm guessing that's the place for Lana's trial but it still doesn't feel like a huge area).
Most of the areas in SM feel a bit small and not that long. The buildings doesn't give you that massive vibe like the Pokemon Mart in Lilycove for example.