Starting from IVBrige, Intel supports the H264 StereoScopic and Multiview 3D profile decoding. This is bit complex to implement and I'm not sure whether it is worth to add in chromium considering the effort we needed in the media stack. There could be massive changes needed , not just in chromium-media-vaapi path but also in general chromim-media code including demuxers ,parsers and chromium's internal DPB management.

Display side implementation is also needed for blending the multiple views to a single one based on metadata from media side (somewhat similar to HDR). But even without display support, we can make it work with displaying only required views.

Not many videos samples out there which is encoded with H264-MVC/SVC profiles. Nevertheless we have added the support in Open source gstreamer vaapi media stack years ago. So for now we can consider this as a missing feature in ChromiumOS.