I upgraded to Windows 10 on my current PC recently when Avid announced support with for Pro Tools 12.5. I can’t comment on Reaper/Wwise/Unity, but…
I haven’t had any issues related to the upgrade, that I wasn’t already having before it. The biggest issue was compatible drivers for my video card. My computer is VERY long in the tooth right now, so that’s not a big surprise. AMD stopped directly supporting the card a year or two ago, and I was having issues with the card while in Windows 7. Had a bunch of problems with it immediately after the upgrade as well, until I axed all the drivers and let Windows 10 run a generic driver for it. No issues since then…other than those that come with a 5 year old computer trying to run current software. 😉
No issues encountered with any of the other software I run (Native Komplete, Soundminer HD+, RX, all those other plug-ins sitting on the drive).
I’m building a new rig myself right now (waiting for the last few parts to come in). So I’m looking forward to having an up to date computer with a clean install.