Hi openfly. The extra availabliy has already been added. See the following paragraph from today’s FAQ’s:
The additional 500,000 reward seats which are directly linked to the new guarantee have been released for you to book on ba.com for flights departing on or after 28 April 2015. However, some flights may have released the minimum number of seats already and if these have been booked you may not see additional reward seats available on those flights from today.