The cowling of the current turbines serves the same purpose, but needs to cover 360 degrees of rotation, so it's heavier and draggier. The blades have a bit more angular momentum in the propfan than in a high bypass turbofan, but there's fewer of them.
>The cowling of the current turbines serves the same purpose, but needs to cover 360 degrees of rotation
this doesn't make sense. if you are not worried about fan blades flying off in directions other than the fuselage, why cover 360 degrees? (and if you are worried 360, then why open rotor?)
The cowling is its own structural support, so needs to be strong all around, otherwise it would fail on the other side and you'd get blade+cowling approaching the fuselage at high velocity.
Instead of reinforcing the fuselage, I wonder if just having a 1/4 nacelle that shields the passenger side would work.