I really hope this feature will see the light of day.
I don't want to bother my friends on Strava with my lunch walks.
It's pretty clear that it could be implemented on either side. Strava isn't pulling raw files from a harddrive, it's one program talking to another program.
But an implementation on Garmin's side would hide it completely from Strava, whereas an implementation on Strava side would be free to have fine-grained privacy controls and not just an accept/reject switch. So I'd greatly prefer it to be solved on Strava's side.
But user preference is pretty irrelevant to a company that still hasn't grown independent of finding the next investment round. The question is which side has the stronger incentives. While Garmin hasn't much of an agenda other than making the user happy so that they come back for more hardware, Strava, being a social network, has to balance a user's interest (privacy) with the interests of that users peers (seeing what others do). But does that make them more or less incentivized? I still think that Strava should be more incentivized, because the solution to lunch walks is making all your activities private by default and only sharing manually. Which is clearly not what Strava wants.