AAISP say they have no control over who's added to the trial.
The ability for ISP's to add users manually went months ago with only Plusnet taking up that offer.
I was told this as well.
The problem is I was talking with them about it months ago at the time plusnet were adding users, AAISP off the ball on this sorry to say. I didnt post it at the time, as was just disappointed, with the price point they at and their reputation for been in the lead in this sort of thing, and it turned out to be quite different.
Also the trial was suspended and then resumed, so that had an effect on things as well.
Cannot say I am too surprised at only plusnet taking it up though as the lead reason the last g.inp rollout got abandoned was the CP's lobbying openreach to cancel it because they couldnt ride through a short term increase of load on their technical support lines. Its the old lets not upset the apple cart thing hindering progress.