How about a new kind of time limit... When your opponent runs out of time, you get to move again, as in twice in a row. I suppose it could make for some interesting zugzwang-type applications, so if the second player lets her clock run down to nothing also, it's an immediate draw.
To be clear, I think this would stink as a 'changed rule' but might be a semi-interesting variant in the world of online correspondence chess.
When in Pure castled position.... (all three pawns for either side and the rook in his spot)
the 3 pawns can attack an additional rank ahead (the combined threat of a knight and pawn)
this is in the spirit that the Pawns represent archers along the castle wall taking shots at would-be besiegers.
this additional power is lost after the castle structure changes. (which would occur if a piece breaks the castle wall, or after one near/far attack by the archers)
Jeez, this is a fun quiz right or did I miss something?