Don't know how much they have improved, but last year ferried a NEO back from DEN to DFW after an engine swap due to vibrations. Had MX on board, they told me the engine they put on that one was really meant to be put on the one without engines in DFW. They also told me that the 4 flying NEOs we had at that point had had something like 17 engine swaps in the past year. Most of those were not because of failures, but faster wear of some components that could not be done with the engine on the wing. That is of course not sustainable...