I personally hope that planet landing is like the main release. We start with it bare bones and they include free expansions to the paid expansion to include all the various different planets.
That is a possible way of doing it, but it's pretty high risk financially since how are you going to make it clear to the customers when the "cut off point" will be for future updates. Just easier to sell an expansion and say that "this is what you get for the money", with the exception of bug fixes a some minor improvements of course.
If they want to have a steady flow of money into the company without doing subscriptions or going all out with micro transactions they pretty much always will need to have something new to sell. If they would only have two packages (planets, first person gameplay) then that wouldn't be possible unless the cost for these expansions was through the roof (when taking years of future development into account).