Sinisan, you asked about other devices so I will share what I have here. I have a Zidoo x9s, Zappiti 4k (both the 2016 models bought used), rpi3b+, rpi4, shield, and am considering a vero 4k+. I also have an LG 3D TV and a Epsn 3D 4k projector.Firstly, they all play sbs/ou fine, but then, pretty much everything plays sb/ou fine, even my ancient WDTV. Because every 3D TV and projector out there can combine the two screens on their own so the player doesn't do any of the work.
Now for 3D MVC, the only 3D worth watching in my opinion as it's half quality on my TV and full 2x1080p, ie both eyes are full 1080P quality on my projector.The Zidoo and Zappiti both play 3D MVC fine with Atmos and DTSX but HDR support is only at 8 bit I believe and not 10 bit, and the user interfaces/UI are painfully slow. And I mean PAINFULLY SLOW. They can also handle the 4k pretty well. The rpi3 plays 3D MVC fine, fast UI, but no Atmos or DTSX or HDR support and none will ever come because the hardware can't handle it.
Enter the rpi4, which has the hardware for it but not the software...yet. The shield has no 3D MVC support and at least came out and said they have absolutely no plans to support it. But the shield plays 4k stuff on it's Kodi add on beautifully and it's my go to for 4k content. And I use the Zappiti for all my 3d content, because i love it's poster wall. I just have to turn it on 5 minutes before I actually plan to watch something and it's a royal pain to set up with internet and registering requirements just to use it.
My Zidoo eventually died during an update (beware) and was bricked. Of course no support from the Chinese co. who sell this thing. But it was good enough while it worked. The new z9s does the same thing but with a faster interface but after my experience I wouldn't touch it. Zappiti's new stuff has tonnes of bugs and little to no support, they have even closed down their forum because it was so full of complaints, so I would never buy one of their new ones, especially at their high prices.
Now the Vero 4k+ is a British product that has a very dedicated support team. It's 4k playback is great and UI is great. But it only supports 3D MVC on it's BETA os, it is not ready for main release. They are working on it and keep promising a full working 3D MVC 4k os but that has been in the works for over 2 years so who knows. It has a few bugs in it, mainly due to some titles not playing correctly on some TVs, but most people are happy with it and it is the current headrunner in the 3D MVC market. It is expensive though at $220 Cad compared with some of the others and especially with the $100 Cad rpi4.
I currently use my rpi4 as a NAS running openMediaVault to feed media to the Shield and Zappiti and occasionally to run Retropie. I think the real problem with rpi and Libreelec is that they are very cheap, and free, respectively, and the people with the skills to code these can make a lot more money coding for other projects. This is basically a hobby for them, a very very very time consuming hobby. So we non-coders are basically at their mercy until they get around to writing the code, but then, who can blame them for taking so long when their skills are worth so much more. It's quite a cheek to ask someone to work for us for free, that's more of a Liberal Left Wing think. So if we really want it done, we need to donate, or find a rich benefactor. This is one reason I have been watching the Vero 4k+, they, at least, are making money on their product and therefore have the money and motivation to keep going.
Yes it's long and not very articulate, but I also have skills that are worth more than monitoring forums pays:)
Good luck.
P.S. I love my rpi's, all 5 of them, and have no problem getting every cent out of them. One in my Arcade1up TMNT unit as a hacked arcade machine with 15,000 games, one as a remote Christmas light show program using FPP and Vixen, one as a media player for the kids room, one as a portable media player for my SUV, and one as a NAS/Kodi player for my living room. If you are in Canada, I would love to buy yours. They are a time consuming hobby, but so fun.
Reading over this it sounds a little mean. Bottom line, yeah, it really sucks that the rpi4 doesn't support 3D MVC, it would have been the world leader and really really awesome.