LOL, I'm sorry, but this is statement is so full of qualifiers that it doesn't mean anything. You say that it is a certainty that the cruise line will expand . . . but that it won't within the next 5 years, though possibly within the next decade *if* bookings stay solid and other factors. That is not a certainty, you are just saying that maybe five years from now Disney will think about building another ship.
Bottom Line: There is no certainty of another Disney cruise ship being built in the next five years, and you've just made an educated guess more than five years in the future because the cruise lines make a lot of cash, (though there are concerns about cannibalization which each new ship made).
We are talking about the same company that would in theory be paying for both projects, and in the end the money comes from the same pot. You're suggesting that WDW will commence construction on both Avatarland and Carsland, which would cost around $1.1 billion. Look, this is about what DCA 2.0 costed, and while they did BVS and Carsland at the same time, they did Mermaid prior to this, and World of Color prior to this other construction. DCA needed saving pronto, as its financials were horrible, not the same reality for WDW as a whole, and the park that is really getting the focus is Animal Kingdom.
We know that Carsland for DHS has not been greenlit. They probably wouldn't green light Carsland until they had a years worth of data from Carsland's first year, unless they for some bizarre reason made a rash decision.
You can say they are "looking" at DHS expansion, but this doesn't really mean anything, they do a lot of blue sky stuff, and much more is suggested than what is done. Even if they do green light Carsland, you first suggested that construction could begin within months, now it is within the next 12 months.
Bottom Line: You heard that expansion of DHS was being discussed. You are guessing that if they decide to expand DHS with Carsland then construction will happen in 12 months. Of course, such a course of action would necessarily take attention and perhaps some resources away from Avatarland, can't see Burbank doing this until they refined plans for Avatarland.
DCA 2.0 construction was spread out over many years, if Burbank decides to do Avatarland, Shanghai, *and* Carsland at the same time, this would be more construction going on than they have ever done.
Cameron and Disney are aiming to have Avatarland open around the time Avatar 2 comes out. It would be a great way to get synergistic publicity for both endeavors. You can bet that Cameron is watching the timeline and development of Avatarland pretty closely, and having Avatarland open as Avatar 2 comes out would be the icing on the cake.