I am not sure if this is just me, but I have found myself way too many times in this situation: FC company gets together, we do the trials, maybe the weekly Dun Scaith run, and then... we are forced to split because everyone has now to do Light Party roulettes.

My suggestion/request/hope: give us an option for pre-made groups that allows entering content (roulettes included) with Oversized groups. In fact, make it the default when trying to join any non-trial with more than 4 members.

As far as balance goes: give all enemies in the dungeon an HP every player over 4.

5 players = +65%
6 players = +130%
7 players = +195%
8 players = +260%

This should compensate for the increased damage output of the new group setup, plus a bit more to make up for possible increase in-group synergy (like more piercing debuffs, etc.)

Alternatively: it could be done as a group debuff that simply divides the whole group damage by how many more members are in the group, then a notch.

4 members = 100% damage.
5 members = 73% damage.
6 members = 61% damage.
7 members = 52% damage.
8 members = 45% damage.

Not exactly the same proportions as above, but may be easier technically to debuff the players than buff every single critter.

The way I'm framing this, it would be unlikely to be exploitable, rewards would remain the same, you still would get the same amount of drops per run even with 2x the players. It's simply a tool to allow big-but-not-huge groups of friends to play together.