I would love for there to be a way to only enable specific features to the /player command. Things like

• An option to shadow @s only
• A limit to how many fake players someone can make
• An option to only control fake players a player has spawned in

There are more possibilities but these are the first ones I thought of.

1. players can only shadow themselves or others only if they are OP on the server. OP should be good enough permissions to do whatever you need, so don't feel @s would need to be enforced here

ad 2) and 3) there is a merit to both for non-op players. Seems like you are trying to manage a server or rogue free players that are given more power than they should have. Carpet was not written for this kind of case. Seems like what you need is a wrapper command aroud 'player' to limit how its executed - this can be done with current scarpet capabilities.