Earlier quoted context omitted.
Probably when it is used mainly as actual currency, not for speculation or black market exchanges and laundering.
I was skeptical of Bitcoin for a long time, but the other day I was on a (legal) website and they had it listed as a payment method, right next to Visa. Seeing it there really showed me how far it's come.
I mean if some big retailer like Amazon or BestBuy or Walmart to accept it, but only 0.02% of their daily transactions involved bitcoin would that be a success? It's a lot of money in absolute numbers, but it's minuscule as a percentage.
If it were 5% that would certainly be something to look at.