Basically the same idea as EXP: there will be a drop rate bonus that is increased by a certain percentage divided by the number of party members in the party. We can test this using the same values as the one for EXP for testing (around 24% increase for a full party I believe) and fine tune it as we go. This feature will not include characters within the same master account, of course. This could help increase the amount of party play for endgame content.
If the staff wants it to be only activated in certain times of day or make it like the bonus exp system is fine too.