A Ponzi scheme is one where the schemer uses later investments to pay off the earlier investors.
From the 
land claim Q&A, I drew up a list of features they are promising, but haven't implemented yet:
3D Models/Objects: Beacon, Claim licenses
   Outposts:
   Outpost crafting systems
   Outpost modules:
      habitation
      armory
      refinery
      hydroponics
      storage
      medical
   Automated Defense drones
Planetary Weather
   Sandstorms
   Electrical storms
   winds
   snow
   other
Planetary Geophysics:
   Earthquakes
Motion Detection Alerting System
Claim registration system
Space Criminal System
   Destruction of Claim Posts
   Piracy
   Theft
   UEE Protection system, UEE Patrols
   Dedicated Mercenaries
   Private Defense contracts
Land designation systems.
   Available for Claim
   Reserved
      National parks
      Wildlife Refuges
      Nature PReserves
Industry:
   Mining
   Commercial Production
   Retail outlets
Analysis:
   Core samples
   Seismographic surveys
They are very clear that "These claim licenses are being made available for pledging to help fund Star Citizen’s development." In other words, they will use the money to fund the development of features.
Now, if they're using the the money from this sale to pay for the development of previously-promised features, then what you have is not a Ponzi scheme, but the incorporation of Ponzi elements into a different funding scheme, a Ponzi-like, if you will (or a Ponzi-like-like), specifically:
Announcing and selling new features to pay for the development of already-promised ones.
Crowdfunding implicitly monetizes feature creep; by having a continuous funding model, they are continuously creeping.