The problem is that paper gold does not trade inside a lab experiment. He speaks of algo trades all the time, so surely he must be aware that gold could fall victim to a downward spiral in stocks, for example. That correlation has been pretty firmly established by the market. So on one hand, Sinclair is justifiably bullish on gold, but on the other, he would probably acknowledge that many investors could see their account values (in USD) decline substantially should that occur.
I have zero problems with his outlook, but I don't really agree with the expectation that's developed of gold going up in a linear fashion to $1650. I think many of his admirers would be extremely distressed if gold went down to $800 again.