Not any more to my knowledge. But if Orion becomes a success there might be one! (founder here)

Current situation is - WebKit works great on Linux so that is not a problem. We've built WebKit on Windows too and while it works, it's not great. We are talking few developer-years of effort there (performance is main issue).

Why does WebKit perform poorly on Windows?

I do not know, but in Windows tests it performed about 30% worse than Blink (Chromium).

AFAIK the only major contributor to it is Sony.