Long term feasibility is a good discussion to have and I probably agree, I'm just throwing out an idea. More likely a new fully realized park will have multiple lands and themes to to. I have no idea what that would be though. I'm not trying to be creative here. It's a better question for another thread though.
Regarding vacation habits, you already have Disney promoting hopper tickets with all packages, and you see them creating better transportation options. I suspect the only way they build a 5th gate is if they see a drop in attendance and a rise in attendance to Universal. So a 5th gate will probably have better transportation so you have people park hopping easier and more often. You already have packages that give cheap ticket options once you hit the 5 day threshold. I think they'll just want to keep people on property at all costs. You'd need marketing data to see if a 5th gate would get people to come down longer. What is the average stay? 4 days? 5 days? I see a lot of 4-5 day promotions. Why not make it 6 days? People with better data have better answers. I'm just speculating.
I agree on 18 numbers. I can't wait to see them. Want to make a bet on them?
On the theming, I know. I think it's a mistake. In any case, working on that context, I would retheme Sunset at the very least if that portion of the park receives a new land. Maybe part of Echo lake too.