Appreciate your interest for Open64.
On windows port, at this point in time we do not have plans for a windows port for x86 Open64, but will certainly convey the request for internal discussion and decisions.
On other queries around GPU and stream SDK, let me discuss internally and get back to you.
I too really wish AMD Open64 supported Windows. Currently the only decent free alternative seems to be to use Visual Studio Express (does that work properly with Stream SDK? Since I'm as student I have free access to Visual Studio 2010 Ultimate, so I've never tried).
If Open64 was supported on Windows, and was officially supported with Stream SDK, there would be a very welcome alternative to using Visual Studio. Indeed there are pretty few free C++ compilers available as far as I can see. MinGW does not support 64-bit, though MinGW-w64 seems to work ok.
I really hope you decide to bring support to Windows, I know I'd like to use it.