It is an from an internal bmi announcement.
BA's A319's/A320's have a config of 132/162 respectively so an extra 2 rows on the A319 & an extra row on the A320.
I believe the wardrobes/cupboards will be taken off these A/C so in actual fact the seat pitch shouldn't change majorly.
bmi is aiming for a more consistent operation. With all the shorthaul A319/A320's having the same config/seating, midhaul being operated on only A321's & Saudi/Longhaul operated on A330's.
Exciting times ahead for bmi hopefully.