It would maybe help to turn this round the other way.
- The trainer needs controlled by ‘something’
- Trainers can emit data about what they’re doing (eg power and cadence)
Currently most software suppliers control the trainer directly via ANT / Bluetooth and they (where ERG is in use will tell the trainer what power should be ‘set/held’ when the rider is pedalling).
The trainer (let’s say an Elite smart trainer for example) can transmit (often in 2-3 channels or more) what it is then doing.
As far as I am aware the Smart trainers in existence (Elite, Tacx, Wahoo etc etc etc) only emit the actual watts and cadence that they detect.
So to implement that, we’d need all smart trainer manufacturers to start transmitting additional data that they received from the controlling software.
(Caveat: Maybe this does happen, I’m just not aware of that use case being addressed at all - my experience is with Tacx and Elite)
Does that help/make sense?