Serious movement appears to be happening with respect to NV. See videos below cross-posted from this forum thread:
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@XCP-ng-JustGreat Well after over a year and a half and AFAICT not much progress from upstream on NV support for Windows/Hyper-V in Xen and XCP-ng. It is discouraging that support from upstream for this feature has not come yet. So I think we, as users of XCP-ng and Xen who are interested in this feature could roll up our sleeves and start working on the problem again and hopefully jump start the process of getting this feature working in upstream Xen and XCP-ng. I will follow up with another post to propose what users of Xen and XCP-ng can do to help.