Yes it does take extra work. Problem is often that that work was done in the past when isp implemented their ipv4 metodology. And instead of using the ipv6 rollout as a chance to improve their design and operations. They just add ipv6 into their ipv4 design and methodology. They encumber their ipv6 rollout with their decades of technical debt and cruft they have normalized in their ipv4 world. And it will makes things harder for themselfs when trying to turn off ipv4 in the core.
Yes it does take extra work. Problem is often that that work was done in the past when isp implemented their ipv4 metodology. And instead of using the ipv6 rollout as a chance to improve their design and operations. They just add ipv6 into their ipv4 design and methodology. They encumber their ipv6 rollout with their decades of technical debt and cruft they have normalized in their ipv4 world. And it will makes things harder for themselfs when trying to turn off ipv4 in the core.