According to this article:
Opel won't be making a variation, but it sounds like GM has stopped just barely short of saying they'll be building the Solstice.
Quote: "The business case is moving along," said the GM executive, who asked not to be identified. "We will announce the program when we have everything finalized, and we are getting close."
From everything I've seen, I think it's a done deal that the Solstice will be made. The exact details are probably still being worked out, but if they don't anticipate production, I would think exectutives would be splashing cold water on speculation and talking up the G6, GTO etc. The lack of any official denial seems very telling.