Have heard some rumours, admittedly third hand, of EI looking at smaller aircraft; how much smaller they'll go (i.e. anything smaller than the A319?) and to what extent their hands are tied to Airbus remains to be seen, but I understand that they are well aware that an all-320/321 fleet is probably not in their best interests.
A319's might be an option and would have a slightly longer range than the A320/21's (3700nm vs 3000). Although, what new potential routes would an extra 700nm open? How cost effective is the A319 or even A318 versus its bigger siblings on shorter/lighter load routes? Could a 117 seat A318 or 156 seat A319 be operated with 1 fewer cabin crew than a 180 seat A320 to increase the cost effectiveness?
The other option, if retaining the fleet commonality is a key, would be to wet lease in ATR's, Q400's or some flavour of R-jet for the lighter traffic/shorter routes keeping the larger heavier metal for the busier/longer runs.
No doubt, Herr Mueller will have some ideas (at least we hope so).
JAS