it would be nice to know how much energy was regenerated during a trip

Can this even be tracked from the Tesla vehicle data?

Yes. I use "scanmytesla" with a ELM OBD2 scanner and it tracks several battery values such as how much supercharger KW were charged, how much regenerated, capacity, number of full charge cycles, rated range, and more. Tesla already calculates this, so if it can be accessed by TeslaFI, they would not have to "calculate" it, but see it directly.