The more layers you have, the more time you need to convert all of them to IPv6 (from network to all the applications). IPv6 implementations of various things i

The more layers you have, the more time you need to convert all of them to IPv6 (from network to all the applications). IPv6 implementations of various things is always less complete than their IPv4 counterpart. Notably, even low-level stuff may still be difficult to make with IPv6. For example, Linux supports IP equal-cost multipath routing for IPv6 since 2012. Quagga, a popular routing daemon, still doesn't support that. BIRD, another open-source routing daemon, just got partial support for it this year. If your network is relying on this, it's an additional burden to deploy IPv6.