The m.79 reference is to, I suspect, long range versions of the A320 series aircraft. The latest generation of engines on the LR variant brings east coast USA within range of many European cities but unfortunately a heavy aircraft is not going to be able to do much more than FL320 or FL330 by the time they reach the oceanic boundary. Additionally with the slower cruise speeds ie high 70s vs proper long haul types which cruise in the mid 80s, they will be relegated to lower levels by ATC to stop them from clogging up the NAT system thus increasing CASK.
Aircraft design is largely about compromise. I suspect any new narrowbody type from Airbus will involve looking at how the biggest operators of their current generation of narrowbody are using the aircraft, their trend in usage and how that fits into the wider context of global trends and then striking a balance between identified objectives. At the moment I would say that would lead them to focus on density rather than all out speed and range.