Custom Flows could go through an official approval to become available to all users.

One major element needed would be a video demonstration of the flow, ideally done by the flow creator.

Once it is officially added, a user-made custom flow cannot be modified or deleted by the creator anymore, otherwise it would affect other users' workout history when they've used that flow.

The main difference with Custom exercises "Request to add officially", is that here we use the original user video, and mark that user as the "Athlete" for that exercise, so they get social recognition for adding that flow to the library.

Another small extra needed: sequential or parallel execution.