I think the biggest problem with such a design is simply people not being used to it. Once you're used to occasionally being on the left side of the road for thirty seconds twice a day, there's no downside. The first took a long time, the next few will come slowly, and then they'll become just part of the terrain like cloverleafs (bleh). I also expect their acceptance will vary geographically, like roundabouts (still bleh for me, YMMV).