As aging customers, we've long been accustomed to thinking of these things as phone lines first, with an optional broadband connection second.
That thinking pervades BT's thinking, especially their IT ordering and maintenance systems.
I think the important thing about SOGEA is that it reverses this thinking: a primary data connection orderable alone, with an optional voice service. Where the voice service can be an OTT IP service.
The reason it takes a long time to achieve is because it rewrites one of the underlying assumptions of how broadband can be ordered. Or tested. Or fixed. I don't think we'll see those trials progress very fast...