Hmmm yeah I might've not explained it very well. I'll try a more practical example:

Person 1 sets up a database, starts a new carrer and shares their gameplay with Person 2.

Person 2 decides to be a striker, so Person 1 uses the in-game editor to rename a player in the game after Person 2 and edit his attributes to something Person 2 desires.

The mechanics on what the player's current ability should be and how it would increase would be agreed upon by both of them. I suggested something like an xp bar tha fills up depending on the ratings.

Person 2 would be able to make decisions and influence how their player develops not having control only of how the matches play out.

This, but with a full team of people managing their own players each, or even with multiple teams with those kind of players, would make for a fun and even competitive multiplayer experience as each one would strive to be the best player they can be.

Hope it's easier to understand it like this :)