@chenks - regarding the point about elevated priority, I see your point but there may be more to it than that, because of the detailed meaning of the term.
I have Andrews’ and Arnold + BT’s ‘premium’ elevated priority thing. Maybe IDNet has exactly the same thing as AA. Anyway, this is what I think / hope the AA deal is: (AA say that they do not have very detailed info themselves from BT.) Within the BT network between the ISP and the DSLAM, my traffic should take priority over non ‘premium’ traffic. AA say that if their own network is congested then they will drop non premium traffic first.
But to come back to your point. Indeed as you say if all customers buy the elevated priority thing and if it meant merely literally that and no more, then it would be pointless. One thing they could do though is to guarantee to buy extra burst capacity on demand from other providers, and have burstable links and so on. I did not express that very well at all, but I am hoping you get the idea. It could be linked to an guarantee of investment in running a non-congested network.
AA has in the past published stats for internal congestion in they own network. The last lot that I saw showed that they dropped zero premium packets due to congestion. It is not cheap running a totally uncontested network and the AA premium option is not cheap at all.