I don't know, but it seems likely to me that it should be able to sustain a few companies. All the really high end stuff will probably be first party developed (e.g. by NVidia) and not sold to 3rd parties, but there are a lot of places where flexibility is more important than raw performance. It's possible that market will be fulfilled by open source cores, but I wouldn't be surprised if there are some medium sized companies that make a business out of 3rd party custom chip design.