Apart from the integration that's already been built already between several of those systems at great expense because they weren't designed to be integrated.We're still going to have passports and driving licences and student cards and immigration certificates and nhs cards and oyster cards and everything else. There is no 'integration' between these systems.
The government could stop the decades long crossing party plan to join up IT services and they could decide to stop making them all online e-first. They could buck every trend in IT, which of course you're aware of, to federate authentication and authorization systems. It's possible they'll take this wonderful purpose built ID system and then choose not to use it as the authentication backbone for everything else.
They could.

