I spoke to a rep at Wirefly yesterday and they said they had no information on if/when they would have the S3 for Metro PCS. They even checked with their supervisor and he had no information about it either. Told me to call back later next week.
Either way I'm waiting this out. I played with my cousin's S3 today and its great. I also still have a feeling Metro will offer a rebate on this phone at some point once the early adopters phase passes and demand slows down.