Doubling every year is hoping too much.
Somebody offering those returns would be called a ponzi operator.
BTC/USD's average annual change between September 2011 and September 2015 was +334.69%. (Doubling, obviously, would require an annual change of +100%).
If someone told me BTC/USD would double each year, I'd assume they were thinking that future performance wouldn't be as strong as past performance, not that they were a ponzi operator. Ponzi operators would talk-up their returns, surely?