I would like to do something. In theory, there whould be two ways to do this.

Set the intro camera movement in the mediatracker in a way, that the camera automatically ends where the player’s camera then is during the start countdown

or

force the camera mode of the player during the start countdown into the internal camera mode (and set the intro camera end position manualy in the right position).

Is one of these two possible, and if so, how?

Unfortunately, the best you can do is assume the player is using a certain camera and move the intro camera to end close to that player camera's default position. There's no way to force the camera to move to a different position depending on what camera the player uses, nor is there a way to force the player to use a certain camera during the countdown (the earliest you can do is immediately upon race start).