Re: Mapping plan
There is already a mapping from ipv4 to ipv6 - the 6to4 address space:
Every routable ipv4 address has a /64 of ipv6 space in this way.
The way to encourage ipv6 adoption is to make it a desirable feature that users demand from their ISPs... Microsoft do this to a small degree by stating that the xbox one works better with ipv6, but more is needed.
If big services like google and facebook start promoting ipv6, and making new desirable features available on ipv6 first then people will start asking their isps for ipv6, and are more likely to favour providers that are offering it. ISPs don't bother at the moment because its a cost, if they start to lose customers due to lack of ipv6 then they will take action.