It seems though that you can now pay as little as £1 in cash and the rest in Avios and you still earn Avios and TP on the underlying commercial fare. And you can use it for BA Holidays bookings. So for Avios rich people it might allow you to combine with the double TP offer and earn status for little cash but a lot of Avios. Whether it is a sensible approach is another issue.

Edit. Not sure you can combine with the double TP offer as Term #13 states Avios payment may not be used in conjunction with any other promotional offers, unless expressly stated otherwise.