If bitcoin won`t be the main currency use in crypto exchange then ETH might have a good chance of becoming number 1 but in the current situation, it is not possible for a very long time.
So that means it is impossible to happen?because Bitcoin will always be the currency to use in exchange and the proof is the market cap and volume in each exchanges.
But of course ethereum on the other hand will always remain as second position,and also never forget that Ripple take the position of number 2 in ethereum last year for couple of times,so what more how can he dethrone bitcoin?