Kerdunker,
I hate to be a picky person but beware the doors page! The easyJet, most Germanwings and several other operators A319s also have double-overwing exits and nearly all A318 have one - like most A319s.
I understand that Air France, who operate all 4 A320 Family members, also fly the family as one type.
I do not know what BAW will do (when they also fully operate all 4 types later this month) due to the Steep Approach crew-qualification requirement at LCY for the A318. I'm pretty sure the trans-Atlantic, A318, Steep App. crews could do intra-Europe, short-haul on any other family member from an approvals point of view.
Saman