[corty]

Schema versions in AD are problematic. Not every Windows Server version works with every Windows Client version. You always need to consult the support matrix, and for additional software like exchange that uses AD schema extensions, it gets even more complicated. So yes, if you are not strictly standardized to a single generation of Microsoft products, you do need to fight incompatible clients and servers

[jedieaston]

You can join any Windows 2k+ client to any version of Windows Server from 2000 onward, with the exception of Windows 10 to Windows 2000 Server, due to Win2k relying on SMBv1 for stuff. If you activate SMBv1 on Windows 10 it will join fine. Schema extensions are a different story, but I'm almost certain that nothing in that department has changed since Windows Server 2012. If you are doing a new Exchange install now and can't buy some upgrade licenses (or get an EA with Microsoft), you probably should be on Office 365 anyway.

There's issues with Windows Server, sure, but AD and its relatives aren't one of them.