There's a lot of research going into Additive Layer Manufacturing for airframes - I just came back from a spectacularly boring trip to a PhD conference at Airbus in Filton (where they make bit of the A380 and A400, in particular), and a good percentage of the postgraduate student funding is going into ALM related projects. The / a main problem seems to be that a lot of the properties of such materials are unknown - for example, the way a lightning strike affects an ALM composite surface is vastly different to the effect on standard metal airframes.
You went to Airbus Filton? I'm jealous now, no matter how boring it was!
Kidding aside, a considerable number of airframe components are currently still made by CNC milling, so raw material costs are terrible on those. 3D-printing could improve a lot on that. And then there's the fact that you can easily make any complex shape you want, without manufacturing troubles or remaining stresses in the material. This has the potential to drive part numbers way down, and thus weight and complexity. And in general, even for parts that don't have these special issues: tooling, jigs, moulds etc. is still a large part of the manufacturing cost, as airplanes are made in relatively small series (a few thousand, max). 3D printing offers great cost reduction in that area as well, as the 'tool' (the printer) can be reused across different airplane series and even different industries altogeher (you could print car engine blocks together with landing gear parts, for instance).
The main thing with printed materials is that they're usually anisotropic, they don't have the same material properties in all directions. So they're more difficult to design with. And, like aldo said, there's still quite a lot to be researched on any new material. It's one of the main reasons why composites are taking a while, as well. That being said, the experience with composites should enable quicker spread of printed parts in the future
Anyway, back to topic: are those cruisers hollow inside? By the size of the supports, I would assume yes, but then again that would make them rather fragile, no?