In a recent BT PLC financial report, BT Retail and PlusNet figures were combined.
I would suggest that this is the first step towards a single broadband company in the future. Where a firmware has had two separate competing companies in the past, they have normally merged it into one at some stage.
If PlusNet start to offer their own YouView or BT Vision product, I would think that it will not be long before one or the other vanishes.
I'll give it 2-3 years.