They're getting more confident every day that they will solve the vacuum lift problem:

http://www.defenseindustrydaily.com/walrus-heavylift-blimp-getting-off-the-ground-01103/

A vacuum has the potential to lift more weight than Hydrogen or Helium, but there's a problem with displacement. It's dubious as to whether a material can be developed that would be thin enough which wouldn't collapse after everything is pumped out.

But I just had a different idea. Why not create a double shell? Put Hydrogen in the one in the center, then create a vacuum in the outer one to prevent the Hydrogen from igniting. Prevent it from collapsing with a Carbon Fiber skeleton. Think it would work?

BTW, here's a cool airship concept:

http://www.airship.org/rocket_airships.cfm#rocket