what was the critical point above which the internet was officially mainstream?
The answer is only known in retrospect.
In terms of the internet, I would say the web became more mainstream when browsing services like AOL dumbed down the concept of being online to people making it a "no think, just point and click" zone.
I think systems such as CoinBase have been trying to do just that, but it's not quite there yet.
The internet took quite a while to become mainstream but technology moves 10 times as fast nowadays, not to mention obviously bitcoin is built around the internet. There will be services or payment processors that make it easier for people to use that's for sure. I don't think it's as complicated as many people make out though.
I agree, it's not as complicated as people make it out to be. But, neither was/is the internet.
The internet went mainstream in two phases as I see it, phase one took place in the 90's. Phase two took place with social networking which brought everyone who was late to the table and it nailed that door shut. Everyone is here now. Unless you are poor. But zuckerberg and his drones are taking care of that. LOL
Either way, it was AOL making "retard proof" GUI's that really stuck the internet into the mainstream. Technology is much faster these days, because people are using it....but look at what majority of people are using...easy simple apps that a 3 year old can operate - so much so that some even predict apps could become the death of the web browser and traditional internet.
Ease of access with make bitcoin go mainstream, as I said, coinbase as already kickstarted this ease of access. It's the long wallet keys that intimidate people who are not "in the know" with coins.
This is the pivotal point of bitcoin going mainstream...When AOL made retard proof GUI's and people hopped on, they were not really using the authentic internet - it was watered down and kind of disguised. This will happen with bitcoin, there will be a retard proof way, people will log on to use it - and at that point, people who were already using bitcoin will slightly judge them - the same way computer geeks turned their noses up to AOL.
Just my two satoshis. LOL