the x265enc encoder was updated this month to support alpha channel encoding. This is a very nice feature and I hope it will enable streaming h265 videos with alpha channel, for example using webrtcbin.
https://bitbucket.org/multicoreware/x265_git/src/Release_4.0/doc/reST/releasenotes.rst
Will this update be integrated into the GStreamer Plugin and will it be possible to use the alpha channel feature? I think it would also require adding YUVA or RGBA to the sink pad formats.
disclaimer: I am not very familiar with Plugin Development for GStreamer, just using it right now.