We have large-scale deployment already.
Looking at the Google IPv6 stats, we can see that IPv6 is already used by nearly 4% of users globally. This number has more than doubled compared to one year ago. These statistics show actual enabled usage, showing that everything from end device, router, ISP and the route to Google supports IPv6.
More significantly, there are some countries that have a much higher IPv6 user share. The USA and Germany have around 8%, and Belgium already even has 20% IPv6 users, and Switzerland 10%.
In my view, the number of IPv6 users in most developed countries will easily be above 50% by 2020. However, I would consider even a 4% share of all internet users a large-scale deployment, so I would consider anybody choosing any option other than "before 2020" as misinformed.