I just found this Thread and would like to state, that 3D mvc support is an essential feature for me too. Thanks for explaining the technical difficulties. I really hope this can be solved at some point in future.
I enjoy watching 3D movies in my home cinema so much. But as long as there is no progress I'm forced to stay with my (already slightly under powered) Pi 3 B+ and LE9.x. So come on, devs. 
The 3D hype on small size TVs may be dead but there are so many home cinemas out there with beautiful large 3D screens and all major projector brands are still supporting 3D. Please move this issue a bit forward on your todo list.