So, from a business perspective, the optimal strategy is to delay the transition (and the ongoing maintenance costs) until IPv6-only customers become a quantifiable number (e.g. you could say that in 5 years about 5-10% of your target audience would not have IPv4, so switching to IPv6 would increase your sales by X%). You can't blame businesses for doing that. You don't play by these rules, you end up one of those companies blogging how they are forced to shut down despite having a marvelous and very sophisticated product.
That said, you can change it very easily. Just offer IPv6 traffic at a slightly lower rate than IPv4. So every IPv6 packet costs you less than the IPv4 one. For unlimited connections, offer some rebate based on the fraction of IPv6 packets, or something. This will immediately put the incentives in the right places and the switch will happen at exponential rate.