Unfortunately, I don't think a Saw 8 will happen. Saw VII promised to wrap everything up, and while it didn't deliver on that promise, most of the details left unanswered were very minor.
Like it or not, Hoffman was as integral a part of the last four films as Jigsaw was to the first three. Without either, the film just isn't interesting or worth pitching. History says the producers certainly wouldn't be against retracting their statements that Hoffman didn't survive the bathroom trap, but how does he get out? It wouldn't be an Eric Matthews escape job, I assure you. They wouldn't recycle that one. Hoffman had no friends or accomplices, so nobody is coming back for him. Without Hoffman, there is no Saw VIII and the producers backed themselves into a serious corner by chaining him up and leaving him for dead in the bathroom.
The questions still remain about why Gordon helped Jigsaw, but that backstory alone could not survive without a main antagonist. They killed off the primary villain. Making a "new Hoffman" at this point in the series just doesn't seem possible and wouldn't make sense. Hoffman wasn't very well accepted in Saw IV but built steam over the course of the next several films to become a serious villain.
As sad as October 2011 was for me without a Saw film, I just don't see a Saw VIII happening. What's more sad to me is that we were all cheated of the eighth film when they decided to cram it all into the seventh. It somewhat ruined Saw 3D for me, because now every time I watch it I find myself wondering what I'd have been watching instead had they chose to go with the original plan of a VII and VIII to end the series.