My unlocked 925 run the technical preview, not the smoothest experience, but maybe because the Windows 10 mobile is still not yet finalized, so hope with the final product it will be more optimized.
Officially? That will depend on T-Mobile most likely. Am I confident it'll happen? No.
The Technical Preview, when it gets to a point where I am comfortable recommending it, can become your upgrade path, and may be the only option for people in the US, without an unbranded device.
Curious if you did an upgrade or a clean install. I did an upgrade on my 920 first and had all kinds of problems. Tried a clean install and it's running beautifully.