CryingLoser: I see your point, but I fully agree with Ceiter's and Abigail's objections. A common practice in challenges for top position is that the leader can choose the type of match ; if he chooses a 21-point match with 14 days per move, it is pretty equivalent to declining as far as a change in ranking positions is concerned. And one should not try to make rankings appear more meaningful that they are. They are not ladders, and they are not even always fair (the problem of multi-points matches has never been addressed). The #1 is not necessarily the strongest player.

Still, you are right that the tendency to sit on a top position (or whatever position) is bad for competition. To avoid that, I would suggest setting as default a ranking list of really active players - that is, lowering the 6 months limits. This does not exclude the keeping of a ranking list of less active players.
As for people keeping artificially active by playing clones, this should be forbidden by the user agreement and people doing that should be rating-banned. I feel that the playing of clones is mostly used for an artificial rating increase anyway.

There is still the possibility of playing only very low-rated people, keeping active at low risk. To avoid that, the answer would be the tried and true Glicko rating system, which keeps a more realistic measure of activity ; in that system, when the rating difference is high, the measure of activity increases by almost nothing.