With Bitcoin, the "penny people" already had a couple of chances to cash out, broadly speaking. Maybe someone will estimate, by studying the BTC transactions, how many ETH people would cash out at various price levels, given the past behavior of BTC, given an equal increase in value. So maybe 30% of early adopters sell off after a 10000x increase, and then you could try to predict when people will start to dump ETH, ceteris paribus.