Knowlegde growth may be sustainable, but it is also impossible to grow forever. (Supposing knowlegde is finite, which is, as far as I see it, the case as long as we make the definition of knowledge depend on characteristics like repition-free and new. For example, you could learn the number pi to even longer lenghts forever, but doing that is not necessarily something new to know as it's just a manifestation of a repition which was already discovered.)
I'm intrigued how you would explain that economies could grow independently of resources. From my perspective, it looks a lot like each and every form of economy relies somehow on some form of resource or resources. As resources are finite, economies can't grow forever.