The problem with this kind of feature is the heavy calulation overhead. To calculate a player's Elo, we need the Elo of all his opponents in history. The Elo of the opponents is affected by the Elo of their opponents, etc. The current calculation time is not too crazy, only some seconds. But if would have to be done every time someone adjusts the list.
However, as so many people suggested it, I might implement it with a bit of caching...
Possible filters would be:
- Tournaments included/excluded
- Time frame
- any other ideas?
Maps maybe, but i think those are the major ones