It feels more sustainable this time. Let's hope it remains fairly bullish and doesn't become full-blown boom-and-bust FOMO again.
Exponential gains like 2011, 2013, and 2017 are never sustainable in a short term sense. If BTC does another 15-20x above the previous ATH like past cycles ($300-400K) then it's going to crash hard again, 80%+. There's just too little liquidity, too much profit on the table, too much emotion, for price to calmly plateau after gains like that. Volatility begets further volatility.