I don’t know - I think this could be of use and wish more watches extended it out - with the appropriate reminder when toggling it that will not be as accurate as manually starting activity.
But can’t see why can’t go the route of Apple Watch for example where you get a reminder saying - did you start x activity - if yes confirm to continue. And if you have started and are still for any period of time - a reminder that you are still tracking and do you want to stop tracking.
Could even add in options like if you say yes to tracking then watch asks to pause to get a solid fix or even show level of fix.
When get stop reminder could add option like resume later (turn off gps) for example.