Hi Pierre, Welcome to the one world-wide family WikiTree!
We all share all the profiles on WikiTree. We should not add private codes that are only useful to individual users. Your sequence number idea would not be useful for everyone. They would best be used on a private desktop computer program of your own family tree.
Part of the problem is as other profiles are connected to your family twig, or as your twig is connected to surname branches, the numbers will change. You will have to constantly renumber your ancestors with each change.