Just to add: We reported the issues we found to Microsoft, and they confirmed them and told us later they have been fixed. However we don't have the bits to verify this, so no guarantees.
The main issue we found with the non-native compiler. For the most part, if you enable the .NET Native compiler (typically using the release configuration or enabling it in your project settings), things seems to work, however note that build times are much much slower. Also note that running on a Phone doesn't work at this point at all.
As Rex mentions, we haven't done any full certification and can't really begin this until Windows 10 is final, but we've done what we can wrt to reporting the issues we found and have been working closely with Microsoft on this.
The next major release (AKA Quartz) will have support for UWP out of the box.
