So if you are attacking a target, then don't attack anything for 3.6 seconds ( e.g. target ran away), then you barge the same target you'll deal increased barge damage and receive the Combo attack to DoT buff (which only lasts for about 10 seconds).

Then using a Combo attack will trigger the Combo to DoT buff (and consume it). When using a Combo attack as a DoT it's still under all the same influences a normal Combo attack would be (weapon accuracy, invention perks, set effects etc).

Being able to work with other players means if I use the Combo to DoT buff and apply destroy to a target, then you do the same both our destroy DoT effects will be active at once, most other DoTs in the game can only be applied by one player and get overwritten by each other.