Cheap international transfers, routing around capital controls and avoiding dragnet monitoring of cross-border financial transactions, i.e anything cross-border is the killer app for bitcoin right now. imho.
Front-end tools for cross-border end-user btc wealth management are less than stellar, i.e. non-existent.
In my view the "killer app" is managing wealth past death duties. Cross border is important, but I see it as 2D space: adding generational time opens up 3D power.
When the moderately wealthy (say property devs or mainstream entreprenuer types around $5-20m) realise that the 'coin can give them the kind of planning previously limited to serious money, they'll be piling in. And in aggregate that's a lot more new money than the odd marquee name like Branson.