Not all customer use the DNS Server from the system. Especially bigger companies use own DNS Server. There it's difficult to move the website without downtime.
It would be great if it's possible to have the option to move them so that the website is at the new and the old IPs available. So they can change the DNS when they have time, the website keeps online and the old data can be deleted after. Of course there is a risk of data loose if somebody makes changes at the old server.
