If you advance the timeline after that odd, fragile moment, you close and resolve the questions. You make things... boring.
This is simply not true. Advancing the timeline doesn't have to mean that you close and resolve the questions. Like, for example, it doesn't have to mean that by advancing the timeline you solve the riddle of the Mournland's creation. In fact, WotCs decision not to advance Eberron's timeline for me was just another nail to the 4E coffin, because with the 4E version just being a rehash of the 3.5 one, I simply had no reason to buy 4E Eberron products.
But even if it closes and resolves a question, that doesn't have to mean things get boring. Let's just assume you remove diabolism and Asmodus from Cheliax, this could lead to a lot of highly interesting new situations. You just have to look at our real world's events to see a lot of countries where overthrowing a tyrannic regime made things worse instead of better. Fukuyama's End of History was just an illusion, and I guess that the Paizo authors wouldn't do something on this scale if they hadn't a plan for the time after. History wouldn't end there either.
And you can say a lot of things about Faerun, but even the 4E realms were the opposite of boring and held a lot of opportunities for adventure.