I would really like a "Ready Check" feature.

Something like the party leader presses "Ready Check"
-A small dialog box appears in the center of your screen asking "Are you ready?"
-Clicking yes puts a dot next to your name that turns green
-Not clicking or clicking no puts a red dot next to your name

This would help out greatly considering endgame events and other things that take time, you have people AFK or are not paying attention etc