It would be neat to be able to queue up into a random lobby with another player for raiding as a duo.
This could make it a little fairer for the single/duo divide so that builders can have duo's in mind when they build their outposts, with single runs still available for those who want a challenge.
I also feel like the game would probable see more longevity as a real multiplayer experience, because I'm personally getting a little bored of raiding outposts over and over by myself. Some outposts are pretty interesting, but a lot of them are very samey.
I was wondering what it was that was so different to the DBD experience, which is also very much the same from game to game, when you get camping/tunneling killers and genrushing/hook-mobbing survivor teams, and I'm pretty sure it's the direct player interaction.
Having a live player present when raiding makes it a lot more interesting, and would ultimately get more people raiding more often, helping to solve the raid-build ratio that seems to be screwing over builders as there aren't enough raider to fill them.
Additionally, duo's seem to give you a lot more deaths than single raiders, they play less cautiously and aren't as penalised by dying over and over.