As far as I've seen, that is just being spread around by Darvin3 and others in that group of posters. Not saying it's true, just that it's speculation at this point. I mean, why wouldn't they make a sequel to the Fantawesomous game we all love?
Officially, there hasn't been a single peep of news about the plans for Sins since the last patch back in February/March. It's possible that Sins really isn't a game that everyone loves. We love it, but perhaps it doesn't resonate with 90% of all purchasers. Hence, there may not be a Sins-2.
Producing a Sins-2 seems like a logical path to take, but who knows. As far as I know, Ironclad is now working on a land-based RTS.