Very good remarks
edmundronald I could not agree more. Same reasoning for us Controllers, ability to recover automation failures is almost nil. The good old adage : automation "de-skills" is not only correct but frightening since it is this de-skilled " magenta" generation which is currently training the young ones entering the profession(s).
On the ability for ATC to see the mode S parameters , ( the so called Enhanced FMS parameters) my center use them very successfully since a few years . The parameters downlinked are IAS and Mach number, Magnetic heading , vertical speed ( but very unreliable ) and the selected altitude ( the one the crew enters on the FMS) this last feature has almost eliminated levels busts, as a warning comes off on the ATC display when it differs from cleared FL by ATC .
As to the vertical speed , it is very unreliable due accuracy of mode S (25 ft variations) it is common that short variations , especially in turbulence can send messages with 10.000ft VS. This is most probably why we see 30.000ft on the ADS-B diagram posted earlier. I would
think it might be a brief acceleration, but not a continuous descent at that rate . This is why ADS-B readouts , and especially those from FR24, are not a good source for incident/accident investigation. To get a general idea , yes, but not much more.