If I understood well, the "Looking to Play" feature has no effect on the rankings, right?
Our players want to find other players within the ranking, so that they can jump to higher positions on the ranking. It is not a problem of not playing, it is to move forward on the positions.
Due to this, I really would like to push for the other suggestions, namely:
1. Loser has an "idle time" after a game
The idea is to have some time during which the loser remains "idle" for X days, after finishing a game. The goal is that this player is available for being challenged during these X days, thus allowing other players to challenge him. The winner does not have this "idle time", as a benefit for winning the game. This solution will allow more chances for lower ranking players to find challenge opportunities.
2. Not able to challenge too many times
In this case, the idea is simple. If a player challenges more than Y times, he has to wait for a period of Z days to be able to challenge again. For example, a player that has played 3 games, him being always the challenger, he has to wait 5 days before being allowed to perform a new challenge. Of course, during this period of 5 days, it is likely that he will be challenged by a lower ranking player.
But having more challenge opportunities is not necessarily good, specially if they are more than what the members can actually play. What is the benefit of having a lot of challenges, if you don't have the time to play them all?
This might lead to more declined challenges!
I agree with Luis SC idea, to have an atacking challenge and a defending challenge. It would solve the problem of not having avaliable challenges for long periiods of time, what can be very frustrating.
The (lets call it like this) «Idle» solution is also interesting it would benefit the winner (which is fair) and have the looser avaliable for challenges for about 3 or 4 days, letting the ladder flow with more intensity, mainly for the players in the lower positions.
I agree with both solutions (don´t know which is easyer to implement) and prefer them to the idle time after «x» challenges.