Who here is of the perspective that players who do not play for significant amounts of time should start dropping in rank?  Doing so automatically clears the leaderboards of dead players, allowing for active players to take their places.  It also encourages elite players to keep playing, as inactive elite players are quickly removed from the boards and replaces with active but weaker players, who can then be squashed by those elite players who keep playing.

1 Week: Lose 20 ranks

2 Weeks: Lose 40 ranks

3 Weeks: Lose 80 ranks

4 Weeks: Lose 160 ranks

While the losses here might seem high, after the elimination of all the inactive players, I suspect it will be much easier to climb up the ranks again.