The variability doesn't come from the process only but also EDA tools because some layout effects are too complicated to model. Moreover, the variability requires wide range of design margin which seriously hurt the production cost.
I have noticed that what happens in the foundry influence a lot. I would have liked this to come from the foundry consortium. There are many things that go wrong when a chip enters a foundry that modeling could just be a waste of time.
For this service to make sense you must be tied very closely to the foundry. There has been number of companies like PDF Solutions that have been offering yield enhancement service for years. What is different about GSS? Kris