When wiil last party upgrade DLC will be added?

Party citron and Party imp were bot already in a DLC for summer nights event which was back around July, sorry you may be waiting a real long time before they come around again

also, I might not be completely sure about this but EA did not actually put details for this limited time DLC on their news page. they didn't even post about the afterparty upgrade, (which was party corn and partybrainz) the GW2 admin were very quiet during those months due to who knows what.