Update:
I've been using RW on my laptop since the preview started. Had zero issues.
It's been a few weeks, and I'm putting in all the SR Missions for Season 5 that I own. I've had ZERO issues.
In fact, it seems to run slightly better under Windows 10 than 8.1/8/7.
This is of course not verifiable, but my main PC has RW installed on a SSD Raid 0 Array (2 SSD's, striped for speed). My laptop is running a laptop HDD. Can't remember the speed, but not awesome-tastic (it's not even a hybrid drive, just a plain old HDD).
I swear to Nuffle, that the Laptop was opening, loading, and performing better under Windows 10 than the PC under 8.1 90% of the time.
OH, and the PC is WAY better than the laptop in all respects.
PC = 4770k i7 @4.0 GHz threaded (stable OC'd at 3.0), 16 Gig RAM, Geforce 700ti
Laptop = 4720HQ i7 @2.6GHz, 8 Gig RAM, Geforce 960m
I upgraded the PC to 10 and it destroys RW. Loads huge realms in about a second or so, duplicating topics is about .25 seconds, etc...
All in all, if you're a big RW user, in there all the time, and you don't upgrade to Windows 10, you're shooting yourself in the foot.