Like in the title. With E-ELT we are pushing the limit of what we can build on the ground. With JWST we are pushing the limit of what can we launch into space.
So instead, why don't we launch tools and materials to build a telescope and polish its mirror in orbit? This has several benefits. The environment is vacuum and microgravity, so very large components can be moved with small and light tools. The structure can be very light and fragile, bacause it doesn't have to survive the launch. It can be huge, because it doesn't have to fit into a rocket. Errors can corrected before it is commisioned.
I am sure, I'm not the first one to have this idea, but I failed to find any existing projects (upcoming or future) on the web. Do you know any such projects being considered?