Today I installed bootcamp. It did not go as smoothly as expected. Although Apple's support documentation at the time of writing just said follow the upgrade path and will all be good. The Intel Iris 5100 was the cause saying it it was not compatible. I do admit I was going from Windows 8 rather than 8.1 straight to Windows 10 as I had retail media, and did not want to patch upwards all day. The other strange thing was the apple supplied drivers were the same for both Windows 8 and 10. Still after much fiddling and failed upgrades I found a solution.
- Setup BootCamp in usual way
- Create USB software key using the download software option
- Install Windows 10 with keeping files only.
- Install drivers from the driver folder first
- Install BootCamp Setup
- Done :-)
This will cause you to loose all your applications so it may not be the right choice for all folk. Unfortunatly it was the only way I could get it to install properly.