I have to agree that version 3 would be my preference as well.
With that said, I can't really see how this design is superior to a Six Moon Designs cuben fiber Haven Tarp paired with the Haven NetTent. They look... um... pretty similar to me...
To be fair, the Six Moon Designs version weighs 26 ounces and costs $610 for the pair of items, so the Zpacks Duplex would ostensibly be lighter and (probably?) cheaper.
But the SMD NetTent has a silnylon floor, which seems like it would be substantially more durable than a light cuben floor. The cuben fiber Haven tarp is also 0.74oz/sq.yd. cuben material vs. the (I'm guessing) 0.51oz/sq.yd. cuben material used in the Duplex. The SMD Haven NetTent also has (what look to be) bigger doors, but the Duplex is taller and wider.
So in reality, this really isn't a completely apples-to-apples comparison.
Still I have to say that if I was purchasing one of these two options today, I'd probably go with the Six Moon Designs Haven combination.
With all that said, it's worth remember that these Zpacks Duplexes are just prototypes, and it's a privilege that we get to see them at all. So kudos to Joe at Zpacks for giving everyone a sneak peek at what he's working on.
I personally hope he eventually adds the Duplex to his permanent product line so there is a shelter system out there that competes head-to-head with the SMD Cuben Haven + Haven NetTent, because that combo sure is expensive!