The 757 is out of production, although the tooling is in storage somewhere. Restarting production would be a huge undertaking by itself, not accounting for modernizing the airliner. It's all blueprints on sheets of paper. And Airbus could quite easily answer with a rewinged, slightly longer A320 (the long-rumored A322) that they admitted to have worked on... Although so far Airbus seems content with just the A321NEO-XLR: cheap to develop, and good-enough to replace most 757 out there (more or less, depending on the model of 757 and the route).
A modernized 767, on the other hand, could be a winner: it's still in production as a freighter and has been modernized for its military variant (KC-46A Pegasus). It's smaller than the 787-8 so wouldn't canibalize sales too much. On the other side the only Airbus competitor is the A330-800 which is too long-range optimized (and thus large/heavy/expensive) to be competitive against a hypothetical medium-haul optimized 767. Really the A330-800 is not even competitive against the A330-900, Airbus shouldn't have built it at all, if you ask me...
The 757 is out of production, although the tooling is in storage somewhere. Restarting production would be a huge undertaking by itself, not accounting for modernizing the airliner. It's all blueprints on sheets of paper. And Airbus could quite easily answer with a rewinged, slightly longer A320 (the long-rumored A322) that they admitted to have worked on... Although so far Airbus seems content with just the A321NEO-XLR: cheap to develop, and good-enough to replace most 757 out there (more or less, depending on the model of 757 and the route).
A modernized 767, on the other hand, could be a winner: it's still in production as a freighter and has been modernized for its military variant (KC-46A Pegasus). It's smaller than the 787-8 so wouldn't canibalize sales too much. On the other side the only Airbus competitor is the A330-800 which is too long-range optimized (and thus large/heavy/expensive) to be competitive against a hypothetical medium-haul optimized 767. Really the A330-800 is not even competitive against the A330-900, Airbus shouldn't have built it at all, if you ask me...