I've been through 7 or 8 centralisations, every one of them sponsored by the business. They weren't done to improve the IT, they were done to make costs savings. So they'd gone down the route you suggest and to avoid the problems you describe. But people and kit naturally proliferate in such an environment. Because there is no central control, solutions are targeted against local needs, not those of the overall business.

To me there's no real difference between say some guys setting up a data island, because they can't get resource from central, to the local IT unit going off on one and implementing some thing non-standard, except for scale.

Centralisation / de-centralisation is a reaction to a symptom. The only guarantee from either is that the next big management idea is to reverse it.

Oh, and I'm not allowed to satisfy the customer, I've just been centralised.