All the 'puters in my place that I activated the upgrade on got the official Win10 downloads pushed to them yesterday (in a hidden folder "C:\$Windows_.BT" - about 6GB depending on your edition). Just waiting for M$ to kick them off.
y'know the Win10 preview has been out there for a couple months. I've been running it on the fast track in a VM since Microsoft made the preview public. I've never bothered to run rohan in it though. Could prolly give it a try today. I'll update THIS POST with my findings.
--- edit my results after a quickie test ----
Caveats:
1. This is running in a VM!! Rohan's GameGuard has never known for playing nicein a VM. Bad Rohan!!
2. This is a virgin Windows 10 Pro image. There are no extra Directx (thouigh it comes DX 12), .NET or any other add-ons.
3. The problem is with GameGuard not the Rohan itself - that leaves out DirectX as a culprit since it is not the actual client crashing.
Bottom line, Results inconclusive. Chances are if you try this out in a 'Real' hardware PC, it will work fine IF you turn off UAC (make your system insecure) and run the client with admin permissions (hand Rohan client godly access to your system).