I'll implement I've implemented an audio sync track using the 1 PPS from a GPS receptor (those pulses are precise to 10 nanoseconds typically). Between each seconds the time of day is encoded into the track and will be parsed in post-production by PPSsoundmerge (a program to be written) that will merge sound clips with their corresponding video tracks (thanks to FFmpeg!) and this, before importing into your NLE.
The DD:HH:MM:SS UTC time of day are BFSK modulated. Initially I tought I would used ASK over FSK so maybe (just maybe) NLE softwares doing wave form analysis syncing could use it (PluralEyes, Syncaila, FCP, Kdenlive, Resolve, any other?). But for now it's only BFSK: I don't want to fight with multiple wave form analysis algorithms from all those NLEs.