Updates on November 3, 2023 (Release 917) updated the LifeMap to no longer rely on rebuilds. It’s all live queries to the database.
I think your proposed process assumes a person starts from scratch and does no repetitious running.
The start/end for each activity would still exist, highlighting your most frequent start/end points.
It’s possible I’m misunderstanding something here.
Yeah, there’s a privacy setting to choose the privacy level for each activity. A person could set themselves as either fully public/private, then switch to per-activity privacy, then toggle particular activities they wanted private/public. One caveat being that these changes are all done in background jobs, so there may be a delay before the setting is fully switched over - waiting some seconds between making the changes will avoid issues with that.
(Under the hood, it’s all per-activity privacy but when you choose Everyone/Just Me it sets that value on all of your activities.)