I could to solve the problem!
At first for testing purposes I installed previuos build of OSMC (2017.10-1) and saw that MPEG-DASH still not working. So problem was not in OSMC.
Then I found Youtube Plugin thread on forum.kodi.tv. There was new alpha build and some userful information.
So to enable MPEG-DASH in OSMC now you need:
- Download and install latest alpha version of Youtube plugin (plugin.video.youtube-5.5.0.alpha17.zip for now).
- Enable MPEG-DASH Proxy in Youtube plugin settings.
- Wait few seconds before that proxy starts.
- Set minimal bandwidth ~30000000 in InputStream Adaptive settings.
All other settings are for you decision.
That’s all!