Apparently the trial is going pretty well. So far, it is having a minimal effect on OTP and apparently plenty of passengers are taking advantage of choosing own seat. All seats are allocated as Someone has already said and a couple of boarding methods are being trialled.
The official line is still very much that this is still a trial but Carolyn McCall has pushed for this and according to the training department it most certainly is a case of when and not if allocated seating is rolled out. We already knew that anyway.