In this model the regions are formed by having local governments voluntarily enter into larger bodies. It's analogous to the way national governments federated to create the European Union.

In this model the people have little direct control over the regions, which is an issue for democracy.

There's no arrow shown coming out of the regions, to show what they control. They might have some control of functions that directly affect the people, or over the local governments that make them up. In fact, I suspect they would be pretty weak.

There's no constitutional change needed to bring this about. In principle local governments could do this now if they liked, and to a limited extent they do.