Mainstream can also mean that it's relatively heard of and popular. It is quite popular in news, marketwatch often has articles on it, so do other financial magazines. In the financial world, Bitcoin IS mainstream. It's just not being actually BOUGHT and USED.
No, because the purpose of Bitcoin is to be used as a currency. We are at a tiny fraction of what is theoretically possible in this regard. So when we are talking about the actual purpose of Bitcoin, we certainly cannot say that Bitcoin has gone mainstream.
Regarding what you say in the OP, I actually think the fact that people are so slow to choose to use Bitcoin because of the myriad reasons you cite is not a problem at all. This has been the fact since day 1, and it is what contributes to the way the boom/bust cycles work. Nothing has changed in this respect... which to me is bullish (dare I say it).
Just because lots of people have heard of something doesn't make it mainstream. The old Native South American practice of shrinking heads is widely-known about, but it isn't mainstream. Although perhaps we should adopt the practice on Bitcointalk!
