The fernata plays correctly when using NWC "play" command, but when exported to MIDI file, and played there, the fermata commands seem to be ignored entirely.
There is no MIDI file equivalent to a fermata so NWC ignores them on export. It has been that way for 20 years.
That is true, but a fermata can have a performance pause associated with it. Might it make sense to insert an appropriate pause in the MIDI file for this? I have since done a little research on standard MIDI files, and I understand now that there is not support for a "pause". Some MIDI file export programs simulate a pause by inserting tempo changes, but this is not a perfect solution.