Im not including third/second world because I think eventually people that don't have access to banks will naturally see Bitcoin as the solution, but as of right now, the average person in a first world country in a regular situation, if they learn about Bitcoin they will threat it as something that is worth holding long term, like gold, but not something that's worth paying groceries for with, or anything ordinary. I mean, why would anyone pay something you can buy with fiat already, without having to change your fiat to BTC, losing money in the conversion?
This is why we need an incentive, such as cheaper prices. Purse.io is the only reason I know of why I would want to pay with BTC. Other than that, I see no reason and I value my BTC too much to spend on "stuff".
Therefore it is established that we need to incentive people to use it.
If we can't find any ways to do so, Bitcoin will remain as a new form of electronic gold with special features, maybe until "Government Coin" is launched and millions of people start looking for alternatives (since with "Government Coin" it will mean physical cash, that is paper and metal coins, will be removed from circulation, this may be the point where Bitcoin goes to 100k+ per coin, since the entire underground economy will not simply stop existing, but it will find its way for alternatives, and Bitcoin will be the best alternative)
But until then, like I said before, I don't see real reasons of why the average joe is going to pay with BTC, specially when they don't get paid in BTC, because if you get paid directly in BTC you are more prone to spend it, since you don't need to do the stupid fiat->BTC->buy conversion.
I disagree with you there should be no incentives for using Bitcoins, Bitcoin is already gaining popularity and it's should be highlighted because it's decentralised, it's easier to use. It's owned by none and it's safe and secure what else incentives you want. Plus it's the risk prone to any outside events. Incentives is a bad idea and it should not be implemented at all.