There was a mod for a FPS I used to play that would remove all weapons for 30 minutes or two rounds if you team-killed.
Maybe FD could introduce a mechanism that limits ship performance, cuts FSD jump distance to 5 Ly, and inhibits weapons for some period? It could then apply to any ship the player is in.
Like I said above, the issue here is that FD has no actual way to identify combat logging. They can tell if the client suddenly closed but they have no idea why that happened. In fact I have had many times where the game froze on me, often during a jump to another system or during the buggy interdiction mini-game, and I had to close it with the task manager. There were even times where I exited normally through the menu and it managed to freeze during the logout process where the client was still open, and I had to close that with the task manger. The game is simply too buggy to make it possible for FD to "identify" combat loggers reliably. If they even tried do to this the player backlash would be absolutely massive, especially due to the number of unfixed (or even completely unacknowledged) bugs in the game. It is extremely poor customer relations to accuse players of using an "exploit" unless you're absolutely certain it was the player, and not a game bug, that is causing the problem. For this reason alone FD will never do anything about combat logging in the forseable future (i.e., as long as we still have game-breaking bugs that remain unfixed which is basically every new expansion).