They ARE definitely developing another vehicle at Pagani motors. Another model, not Zonda.
I don't have the details yet, but they verbally confirmed these at the factory, and I saw some parts in the autoclave area that did not look like Zonda.
Stay tuned for details
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As an aside, they are working on getting US federalization setup for the Zonda. Its currently in the "show and exhibit only" category for US use. It still needs a few things (airbags, etc), but the carbon-fiber chassis should easily pass any DOT/NHTSA tests.