4star
My terminology may be at fault, "conversion" is probably the wrong word. Nevertheless BA is not going to release a A320 type rated DEP directly to the line without some form of training, (edited to add: The training is a handful of sims and line training, so yes, even a type rated DEP does tie up training resources).
As it has been explained to me
recruiting DEPs directly to the 744, type rated or not, avoids some training on the A320 - and the 'bus trainers have already got a busy few months ahead of them.