I'd love to see some CFD of both versions to see whether one solution is better than the other. We've had some cars with a lot of floor exposed last season, but none of them came close to beating RedBull....Ferrari had it for example, but their car lacked overall DF.
Packaging maybe one reason for RedBull being able to shrink the sidepods to that size, but I'd love to see the internals of the W03 to see why would not try to go for such a solution. The back of that RB8 reminds me of top notch up to date fighter planes like the F22...