I know little about IT, but as you say, there MUST be a way that modern aircraft can transmit "burst" transmissions on a regular basis (say every 20min) to home base including ALL the info that would normally be stored on the FDR/CVR?
OK a lot can happen in the 20min between transmissions, but surely a pattern may emerge leading up to a serious incident?
Dating from the early 1960s Lockheed Skunk Works used 'BirdWatcher' on the U-2 and later on the A-12 and derivatives to keep an eye on these aircraft in flight . It effectively tracked disasters - aerodynamic, mechanical or combat related. Aircraft parameters such as altitude, overspeed, canopy off, electrical faults, high tgt, flameout and many more were compressed and then
event transmitted by a short burst of HF to homeplate. When things were going well, the pilot would use the cockpit BW transmit key to signal/authenticate a task done - complete with the flight parameters relevant to that time period. The many Area 51 websites give some insight into this remarkable precursor to ACARS and the satellite monitoring technology of today.
Like so many Kelly Johnson schemes, it worked well in real life. Thus BirdWatcher was able to provide plausible likely scenarios and reasons for the many disasters encountered in the early 1960s.
See
A-12, YF-12, SR-71 Blackbird crashes