Sure, this is really interesting indeed, all ponzi mechanics is open for everyone to see.
When considering the sustainability one should also take into account cash flows, not only the balance chart. If you look at this plot (number of transactions per day) https://blockchain.info/charts/n-transactions?timespan=30days&showDataPoints=false&daysAverageString=1&show_header=true&scale=0&address=1PoNzi7PGzRyvc9KWYBcaauS3oeJqa5vFg you can see that the number of transactions grows, which actually stabilizes the program.