There is no such killer application for bitcoin. Let's face it, Bitcoin's benefits over fiat are currently not big enough to justify switching to it.
I agree. Bitcoin has only some advantages but it is no killer app. It might be difference once governments decide to seize funds or other things happen. But at the moment advantages are rare.
The worse that the blocksize is not raised because when the block is full and constantly a chunk of legit transactions can not get confirmed then bitcoin will become slow, expensive and unreliable on top. I mean who will use a currency where transactions maybe, maybe not, go through?