Others speculate so as well because pf how popular etherium is becoming. Others think that some day will come when etherium will actually surpass bitcoin because of its aspects that are better than bitcoins. Some even claim that btcoin will eventually die because of the many altcoins and competition being created. Bitcoin has slowly become outdated because of its high transaction fees and long confirmation times, and people say that this is what would eventually kill bitcoin.
Ethereum's aspects? The only point of usage it enjoys and thrives on is the booming ICO market. If we look at how governments are tightening their regulatory framework, Ethereum might be up for some harsh times.
People have been complaining about Bitcoin for years, but they still are using it because there is no better alternative. If altcoins were really that much better, there would be a shift happening, but there isn't.
Bitcoin is the first of the first and people value that, where the network speaks for itself as well. Altcoins have earned their place in this market, but as a separate lower division. Bitcoin is on top and will remain there until the end.