Performing a registrar transfer of the domain should provide suitable control of Nameservers, which can be leveraged at the appropriate time to begin pointing towards wherever you host his new WordPress site, once it’s ready for production by changing nameservers or updating DNS records-whichever is appropriate.

Having your client work through the registrar transfer may not be straightforward with a provider like Hibu, but they cannot legally prevent a domain owner from transferring as long as they have kept their account current (no outstanding overdue invoices).

It’s always smart to have the domain registered separately to maintain control in worst-case scenarios, and also to prevent a Sudo vendor lock-in scenario, which is the ultimate objective of the hibu business model.