@raven this is very nice post.
My use case is the treadmill. Usually when you run on a treadmill you get a final constant pace in the watch. You cannot see the speed variations and/or slopes you had in the workout and that is not transmitted later to the application. The workaround is the foot pod (i.e Stryd) but even (the very expensive) Stryd fails.
If the watch is able to see the real speed (and speed changes) or the slope, that changes everything. Because that means real data, not an estimation (with manual changes or created by a foot pod).