I agree with brabazon....this has been a very thorough study. The analysis has been entirely based on cost and political issues such as slots were not an issue.
With a multi-base operation such as eJ, the "complexity" of operating two types is not insurmountable. Key bases (starting with GVA, then moving onto.....LGW, STN, etc.???) will no doubt transition one at a time to an Airbus operation, with crew training etc. taken into account. This has all been factored in, with allowance made for 'complexity costs' etc.
eJ will still be operating a very sizeable fleet of 737's....the fleet size of that will still give considerable benefits.
The traditional cost model of sticking to one aircraft type becomes invalid if a new (and better) product comes along.....do you stick with the old type even if your detailed study says this is the wrong thing to do?
This gives the opportunity to negotiate the best supplier deals....not just for the aircraft but maintenance, support, etc. rather than being held to ransom by a single supplier.
Compared with the 737-700 the A319 offers a wider, more passenger-friendly fuselage, same or better seat-pitch throughout, etc.
Wider aisle and bigger overhead lockers means quicker pax boarding and disembarking. Size and geometry of the holds means baggage loading is as fast or probably faster. (Bear in mind the 737-700 is high enough to warrant a beltloader in most stations, so the higher holds of the A319 is not an issue.)
All in all a better aircraft, a very good financial deal, increased passenger appeal, turnround times same or better, a multi-base environment where the type can be introduced progressively on a base-by-base approach, etc. etc. Sounds like a winning formula to me.
(....and a nice little fold-down table for the packed lunch!)