as someone else pointed out this is IAG buying BMI, NOT BA, i suspect that an attempt to make a "low cost" short haul operation out of BMI may be on the cards similar to Iberia Express, slots could be swapped to and from BA mainline, by keeping BMI a seperate shorthaul business unit could have significant advantages in the future (cost savings in training alone would be significant as there would be nobody moving fleets).
Then of course one could be played against the other, Cabin Crew and pilot unions beware!