True 3D from Blu-ray 3D does work on Plex, but it depends on what device your Plex app is on. I will explain in detail below...
SUCCESS! After numerous attempts, I finally got Blu-ray 3D rips to work through Plex. In order to watch these 3D versions, you will obviously need a 3DTV with 3D glasses, but also a compatible Plex app. I say "compatible," because not all Plex apps are the same. The LG and Apple TV Plex apps apparently doesn't support real 3D (they can be converted to "fake 3D" using the TVs 3D button on your remote control, but it has much less dimension and depth accuracy is often horrendous), however I have found Samsung Plex apps selects real 3D (aka. 3D-MVC). The good news is, if you don't have 3DTVs, glasses, or a compatible Plex app, you can still watch the normal "flat" 2D version from the same file. So, you will always be able to watch these movies, but you will only be able to see the 3D effects with the right setup, including the right Plex app. This eliminates the need for two files of the same movie (one file for 2D viewing, another file for 3D viewing).
Instructions are as follows...
- Use "MakeMKV" to rip the Blu-ray 3D (be sure to checkmark the 3D-MVC codec file too).
- Use "tsMuxeR" to remux the .MKV file to an .M2TS file.
- Add the .M2TS file to Plex.
- Watch 3D movie through the Plex app on Samsung Blu-ray players or TVs.
NOTE: In step 2, move the 3D-MVC codec source file below the H.264 codec source file. Otherwise, you may experience errors when attempting to play the file on non-compatible Plex apps, as installed on Apple TV or LG Smart TVs. I had a "transcoder crashed" error every time, until I moved it down.
NOTE: In step 5, after attempting to watch this .M2TS file through Plex on my Apple TV and LG Smart TV, but not being able to get the 3D-MVC stream to work, I decided to try the Plex app I have on my Blu-ray player. It was a success. The moment I clicked to play the movie through the Samsung app, the system detected a 3D signal and automatically changed the display to output the stellar 3D image. And that 3D image is exactly as it appears on the Blu-ray 3D.
The real problem is why aren't all Plex apps the same? Plex apps on Samsung devices supports 3D-MVC playback, but Plex apps on Apple TV and LG Smart TVs don't. On the flipside, Plex apps on iOS, Mac and Apple TV allows me to change streaming quality from as small as 240p, to 320p, to 480p, to 720p, to 1080p, to the original quality of the file, with many bitrate offerings in between. But, Plex on Samsung devices doesn't offer that feature. I would like to have all Plex apps support 3D-MVC playback AND selective quality changes.
I tried this "3D-MVC .M2TS through Plex" method before, but chalked it up as "it doesn't work" since the 3D effect wasn't coming through my Apple TV Plex app. So, I gave up, not realizing until today, Plex apps vary across different devices. We need consistency and full support for all home theater media.