No inside info either but I could see them making the decision to extend Monsters Inc.’s life so they could punt the decision a bit longer.
I would imagine if Avatar 3 ends up being the last installment in the franchise, it would give Disney pause to start working on a land that would take 3ish years to turnaround.
You have to remember that even though Avatar land at Animal Kingdom came almost smack dab in the middle of the 13 years in between movies, it wasn’t Disney’s IP. So the success of the movie and the theme park land weren’t intrinsically tied together as it is now.
All this to say I think the decision on Avatar 4 and Avatar Land will come in tandem.