Thanks for the feedback, it is always appreciated. With the current tool set still supporting Win7 and Win8.1 images we can't implement that change, as those older systems wouldn't be able to see the secondary partitions created from Win10 systems. In the future when support for those has been dropped or if we release a Win10 only version, then supporting that is certainly something we will look to do. Thanks, Gary Babcock Software Development Senior Engineer Dell | Configuration Services    Dell has created the next generation of client imaging technology.  A cost free tool that will help you quickly create a re-deployable Windows image to be sent to Dell and loaded onto your computers in our factory before they ship to your offices; it’s called Dell ImageAssist.  
With the Creator's Update of Windows 10, you can now have multiple partitions on a USB drive and WinPE will recognize them. This will be heaven-sent for large WIM files. The scenario would be to format the first (bootable) partition FAT32 of around 2GB so you can boot UEFI. The remainder of the drive could be NTFS and contain the image(s). I've manually tested this and it works like a champ. Now, if we could just get the ImageAssist tools updated to handle it so I wouldn't have to split my WIMs anymore. :D Thanks for listening!
When will ImageAssist support multiple partitions on USB?