The list of capabilities specified in the appxmanifest has changed from 8.1 to 10. Some of them apply only to one version or the other, and some of the new ones require the tags be namespaced.
Right now our support is basically to allow a passthrough of XML from trap.xml to the manifest to add more capability tags. But I'm not sure if we say use the new <uap:Capability Name="contacts"/> tag for Windows 10, if that will break a build for Windows 8.1. We may need to be smarter to filter out bad values for certain versions.
Windows 10: https://msdn.microsoft.com/en-us/library/windows/apps/dn934783.aspx
Windows 8.1: https://msdn.microsoft.com/en-us/library/windows/apps/dn423259.aspx
Windows Phone 8.1?: https://msdn.microsoft.com/library/windows/apps/hh464936.aspx#domain_credentials