First let me say that I have just installed Rhino WIP and the QuadMesher command alone is a HUGE thing!
Working back and forth with a subdiv modeler (Modo) this allows a great freedom in choosing the most appropriate approach for each geometry, without having to use plugins or other tools like ZBrush's ZRemesher.
Even at its current state, fixing the problems with a bit of polygon reconstruction and retopology takes just a few minutes compared to the practically uneditable mesh created by Rhino 5.
So, congratulations, and keep up the great work!
If this can be of help, I have made a small test and found that, apart from the missing polys issue, the main thing that is missing is to have clean topology in correspondance of some surface transitions for lower density meshes as well as a system capable of adding supporting loops for small fillets and curvatures.
It seams that at the moment the only way to achieve both these results is to increase the overall density.
In the picture below, in the mesh generated with the lower density setting, the hole/external surface transition is not smooth: it's not very easy to fix and it does not subdivide very well.
If it could be possible to have a circular loop there, then the local detail problem would be secondary, as it would be quite easy to add a couple of supporting edges (like for the top flat cap surface below).
However I'm not sure if the first problem can be resolved independently from the second one.
Please let us know if these types of examples can be of help (in case I'll post the 3dm file) or if you are already aware of these issues and we should just wait for the next update