Interesting idea but even for Easyjet customers you need to have some services (food & drink, car rental, security, etc) that I would not expect to see duplicated between the new and old buildings... Also why spend money in June (see above pictures) for the "old" Easyjet terminal if it is to move in October - doesn't make much sense in my view...
Heard that keeping the unfinished building in shape is costing approx 20mn€ / month - seems pretty steep even by German standards...