The longer runs won't be a problem for the A319.
BMI operate a 144 seat config (2 rows less than EZY) on some A319's which were very comfy even before the new slimline seats so perhaps EI will jump in the middle of the two and ptich for 150 seats?
The A319 at BFS made me interested to see what new markets it could open if the demand existed and EI had the interest. The map below is a quick reference using Airbuses figures for the A319/20. I used the max airframe empty weight and max airframe takeoff weight to make these rough calculations.
Light blue is A320, middle blue is A319.
Great Circle Mapper
If EI were to ETOPS certify an A319, they could certainly operate some transatlantics from BFS without the need or risk running an A330. Places like JFK, BOS, YYZ would all be theoretically possible but financially viable may be a different story.