Single Comment

A weighted history would work with the assumption that anyone who isn't
actively playing games is deteriorating in ability. I'm not sure this is
an accurate assumption to make. Also, the factors you list as causing
performance to drop are going to have less effect on games played on Game
Courier, because these are correspondence games played over a long period
of time, and a person may take time off for illness or disinterest without
it affecting his game. When it does affect someone's games, it will
generally affect fewer games than it would for someone active in Chess
tournaments. Also, the large timeframe on which games are played is going
to make it even harder to determine what the weights should be. For these
reasons, I am not convinced that a weighted history should be used here.

Anyway, if you do want ratings that better reflect the current level of
play among active players, you already have the option of using the Age
Filter to filter out older games. I think that should suffice for this
purpose.