@Jon Definitely a good question and I don’t have the answer but I was thinking that it would work in a similar way to TrainingPeaks where the workout is on your calendar and there is some sort of device connection that facilitates the transfer and then update the SYSTM calendar when it is done.
Found an older post referencing a DC Rainmaker article that talked about their intent to be an open platform but it doesn’t really elaborate on how it will be done but does say that there will be limited functionality.
I only have Wahoo bike computers (a Bolt v1 and Roam v1). The outdoor workouts appear either when I turn on the computer or sometimes I have to force a sync but overall the implementation seems solid.