Who knows how reliable it is, but for comparisons sake - SAH went out of stock with Farnsworth House in... April. B&******.com still has them, and they still float in and out of stores. I hope Fallingwater doesn't repeat that cycle, but I can't exactly say I would be surprised if it did. Arch sets are HUGE sellers at B&******, I was really surprised when I saw how many my local store had piled high pre Christmas, and even more surprised to see they all sold. So they may have a good stock of these piled up. I still think it's a great set and will show good returns, it is just a question of when.
Robie house went out of SAH Dec 2013, and I think by Feb 2014 B&****** was gone - a much higher price point, as Fallingwater is more expensive than Farnsworth, so who knows.
I will say this, if White House ever shows signs of EOL, I may buy a million of them.