there is no one killer app. bitcoin has so many use cases that it will have alot killer apps.
Hope that the OpenBazzar will be a key in launch BTC rocket to the moon! 
You can say that again!
But its not just that, a decentralized marketplace is something that is needed in today's world, it simply needs to exist. Imagine being able to sell to your products to the world w/o having to worry about hefty fees levied by platform operators, or listing censorship, or being able to buy from anyone in the world at discount prices because of the reasons provided above, without having to get permission from anyone?
Its beautiful.