Partition Size Limit for BootCamp for new Mac Pro Machine?
Mac Pro models introduced in 2013 or later do not have a 2.2 TB size limit for 64 bit Windows 10. If there is a limitation with respect to using the Boot Camp Assistant to install Windows 10, then Windows 10 could be installed without the use of the Boot Camp Assistant. Although, you would still want to use the Boot Camp Assistant to download Windows Support Software (i.e. the Windows drivers).

Windows runs on a Mac the same as any PC. Boot Camp refers to several entities, such as:


There is a Boot Camp Assistant application which can download the Windows Support Software and simplify the installation of Windows.
There is the Boot Camp installer, which installs the Windows Support Software. 
There is Boot Camp software installed in Windows that can configure hardware and set the default operating system to boot.
The volume (partition) where Windows is installed is given the label BOOTCAMP and thus is referred to as Boot Camp in the Apple documentation.