I doubt that the aircraft will be an A320neo unless that type offers a considerable commercial advantage by virtue of enhanced field performance. I still haven't found any written evidence of that and Airbus no longer seem to be claiming better field performance for the variant.
Press Releases are always difficult to fathom as the context of statements is never clear. If they really said that the addition of an A320 will produce an "increase of 130,000 passengers to and from the airport ..." then that is four months of SEN utilisation of an A320, not just the school holiday period.
Continued speculation isn't really worth while beyond that but no doubt things will become clearer when any new routes are announced. I have heard Madrid mentioned by the way.