Without a defining killer app, I am confident that Bitcoin will, in fits and starts, inevitably return to its 2009 levels. It would be pointless to guess how long that process will take; or when that killer app will appear although I am also confident it will appear at some entirely unpredictable point.
I don't follow your question. Bitcoin is a currency or an asset class. Does the Yen or the Euro need a "killer app" to be successful or useful? No. QT scan codes already exist, which enable the payment to be recognized.
What's missing that only a "killer app" could provide, and why does that thing that's missing (if something is) drive solely the future success or failure of bitcoin?
Are you saying that business owners don't have an easier way to facilitate payments? Are you saying that mobile applications drive user adoption of a new idea or technology?
Education and comfort level is a big part of this. Computers weren't deemed to be important or a necessity when they first came out. The internet wasn't considered a necessity when it first became available. Education and time changed the popular opinion. The same can happen with Bitcoin...I don't think a killer app is the single solution.
I’m saying that only a killer app will offset the ongoing downward pressure on prices exerted by miners who, faced with falling prices after the China-bubble burst, have no choice but to sell their bitcoins as soon as they earn them. And whales face a related problem: if they sell now, they can still be fiat rich. If they wait, they could end up being fiat poor[er]. Every time the price bounces a bit – it almost hit 300 a few weeks back – they face this dilemma once again and crack under the strain. Absent positive expectations, there is nowhere for the price to go but down, and it could theoretically go down all the way because the system itself could remain fully intact. For miners, sell-pressure is made worse by the fact that mining is much more expensive than it was. What bitcoin needs is an environment analogous to Windows and/or the Mac, which made computers finally accessible to the masses. The Web did the same thing to the once code-driven Internet.
A killer app would change the dynamic from negative to positive. I'm certain it will come eventually but that it could take a lot longer than we think. I suspect that the blockchain itself may turn out to be the bitcoin killer-app, initially as the world's notary public. More and more institutions will use it to keep their archival data tamper-proof, even as they experiment with their own proprietary blockchains. Such use has the potential to ramp up bitcoin use far beyond casual currency-use. I remain skeptical of bitcoin as a day-to-day currency (except on the dark web of course, where I've earned bitcoins myself as an academic ghostwriter).