There are a number of steps required before updating a domain for the managed wordpress sites.

If there was some sort of confirmation before updating, that required you to ensure your changes have been made, then people unfamiliar with the process would be able to avoid the issues that come if you pre-emptively change the domain, before the DNS A record has changed for example.

This would also serve as a helper to know what steps are required before updating the domain.

Alternatively the domain change could skip the DNS check as shown here: https://liquidweb.uservoice.com/forums/909214-managed-wordpress/suggestions/33228178-manged-wordpress-allow-primary-domain-changes-wi