kessje
It think Airbus took some Boeing 737NG customers lately. Pegasus, Norwegian, AA, Turkish and QF from the back of my head. So Boeing taking back some might be strategic.
Qantas remains all-Boeing for their narrowbodies (JetStar are Airbus).
Turkish currently flies both the 737NG and A320 and ordered both the A320neo and the 737 MAX.
Lion Air, Norwegian and American did add Airbus, but they also placed large 737 orders, as well, so they're not swapping OEMs.
Silkair has decided to switch from Airbus to Boeing, so that's one "win" for Boeing I guess. *shrug*