Well, there is a couple of different things that they could do with the owlery. However, what makes the most sense to me would be to knock down the wall separating it from Florean Fortesque's and use it as an extended queue for the ice cream shop. Every time I went to Diagon Alley this year both in July and October there was always a line out the door going along the side and across the entrance to the Fountain of Fair Fortune and Knockturn Alley. It would be an awesome solution to what can become a big traffic flow issue.