You are DEFFINTETLY NOT a candidate for the Insider Program. It's my time to waste if I want and I choose to be part of the Insider Program.
a buildfeed is only a information about a build but you have written like anyone can download it on the www
Somebody has been able to run DISM Restorehealth successfully on this build?, i'm trying unsuccessfully since build 14257, always get error 0x800f081f, even on a clean install, this doesn't happened to me on builds before 14257
I have to say that: Settings | System | Default apps is bugged on that build, even if you choose "Choose default apps by file type". Whatever you choose, it doesn't save, no way! Let's say... Whatever! Fed up of that! Really!
Have you tried doing it offline from the WinRE command prompt (or some other WinPE environment like MsDart) using /Image:C:\ instead of /Online? Unfortunately I can't test it on my system right now because I used Disk Cleanup to remove the $WINDOWS.~BT files. Maybe I will remember to test it for you next build.
No, i don't tried other environments, to be honest i'm not familiarized with anything different to DISM
I remember DISM is really pain in ass, I tried fix it many times, I decide go ahead reformat then reinstall OS. DISM is not easy quick fix.