After spending the better part of an evening trying to get Boot Camp Assistant to install Windows 10 from an Image I downloaded from My Visual Studio (formerly MSDN). I've been able to get Windows 10 installed using the following method:
- Download Parallels 13 trial
- Select Windows 10 installation (a Windows 10 ISO that is 4.4GB will be downloaded to your downloads)
- Run Boot Camp Assistant and use this 4.4GB Windows 10 ISO
The previous ISO I was using from My Visual Studio was 5.02GB, and I'm suspect that the additional space + Boot Camp Drivers that get downloaded may have been too big for the 8GB partition that Boot Camp Assistant creates, hence the error 'failed to copy files'. FYI this previous ISO installs just fine with Parallels, so it wasn't the ISO.
Apple Chat Support noted the issue, one rep said that they've had 5 requests for this in the past few days. They mentioned that there is an internal article about this limitation and that it is scheduled to be fixed with no definitive date. When I mentioned my work around to one of the chat support reps they basically referred to the internal article and said that it wasn't supported on 2018 MBP.
Right now I'm looking to test the new 2018 MBP with Boot Camp as it was either this or a Surface Book Pro 2...not willing to drop nearly $6k on a system that doesn't work, especially with some of the idiosyncrasies that I experienced with my 2013 MBP with Boot Camp.
Hope this helps some of you, and remember your mileage may vary.