BTw were indeed invited into the trial, and as far as I can see it is still subject to mailing lists, but with no criteria to be met.
I think their invite must be more recent. Last year when first released, absolutely no BTw based ISP's were on the trial. I wonder if they have dropped the 1000 figure then based on ISP size. They should have been able to gauge numbers from first stage of the trial. BT as an ISP also has a lot of business consumers.
Actually reading your sentence again and thinking about it, I notice you say BT
w and not BTr.
BTw is a customer of Openreach, therefore any requests go through BTw, which is why the limit could be relaxed for BTw
Its my understanding that one of the hurdles with the first stages of trial is that it was only offered to direct Openreach customers (GEA).. and that is the reason I was given why it wasn't available to any of the BTw based ISPs... including BTr and PN at that particular time.