The negative interest rate is not here to stay definitely. It's just a momentory scenario as the economy adjusts itself these negative interest rate will be gone. But yes for the time being things could change but I don't think BTC would get much of an advantage from this because people still think it of an Ponzi or get rich quick scheme for those who have spare money to throw away somewhere. Equity markets could get more investment and so could bullion but Cryptocurrencies ain't getting that. We need to convince the actual utility of Cryptocurrencies before we can actually expect them to enter this market.