Based on the current market trend and adoption for crypto, it would take something huge. I would say, if this ever were to happen, it would be something from China.
Currently, China is a cashless society with Wechat pay and recently they have invested billions into blockchain technology, the backbone to cryptocurrency.
With how the market is in China, if they decide to lift the ban on crypto and do a 360 turn into crypto and blockchain as a country, they might be able to make something that could take down Bitcoin. This is my own speculations based on the idea that 3/4 of the worlds BTC mining operations are situated in China.
My speculation might not happen due to the fact that the government in China wants to control and BTC and crypto is something they cannot control in terms of value. 0 x