Bitcoin seems to be the past and Ethereum the future.
The question is : when BTC will worth almost zero? Next year? In 2 years?

These seems to be what some people want, most especially those who are fans to altcoins, but I do not see it happening, because bitcoin is more or less like what is still holding cryptocurrency and making it to stand strong. If you talk of some altcoins having zero value, then I will not argue that. Yet there are still very good altcoins in the crypto space.