An incentive? Let's think first about who will provide it. Who will pay for it? Who will organize it? The BTC foundation? Coinbase? Your family? All the users of this forum?
Exactly. So many threads about the same thing. Until somebody spends some casn nothing is going to ahppen.
You are both right that nobody in their right mind will spend his personal cash to advertise Bitcoin in a big manner. But we can all still do something. Start using it, not just holding. If you run a business then give a small discount for people paying in Bitcoin. If you run a Bitcoin company then you could do some advertisement for your business and this would also be a litte advertisement for Bitcoin.
The companies that actually use bitcoin are small companies, if we want for bitcoin to become something that everyone uses and become the best alternative for fiat we need big companies to step up and start using it, like eBay or Amazon to make it as a payment method so that it becomes more popular.
The question is why would big companies want that? It is extra work without benefits. I would not count on eBay, since they are in bed with PayPal. Amazon did not want to because Bitcoin was to insignificant if i remember correctly. We need to use alternatives like openBazaar and if they will become big enough this will not only be good for Bitcoin but also force other platforms to use it.