For reference, next version of CopyTrans HEIC should support the .heif extension as well.
CopyTrans HEIC however doesn't provide any HEVC support, as it's primarily intended as an image codec. On my Win7 system, I have HEVC support (x265 actually) through the popular K-Lite pack, but I'm not sure if the codec is presented as a WIC or a DirectShow component.
Windows Photo Viewer can display HEIF/HEIC files (with CopyTrans installed), so hopefully Opus will be able to do the same at some point.