ETH could never pass the price of Bitcoin.
Seeing ETH pass through bitcoin's market cap is possible but for now I'm sticking to bitcoin and I don't want to say that it won't happen. But I'm pretty sure of that there are a lot of people that are holding ETH and Bitcoin, so it will be a rally against the supply of bitcoin and ETH. ETH's supply is higher than bitcoin but both has been great for this year and as an investment or currency, they will remain well after 5 years.
The supply of ETH is stable and the number of coins mined per year remains the same. In case of Bitcoin, the number of coins that can be mined decreases with time. So if the number of users cease to increase, there can be inflation with ETH and its value can go down. This is definitely going to be an issue facing Ethereum in the near future.
Let's see if that will happen but as long as we are not on that state then there's no need to worry about it. People are faithful with their coins that they are investing and what's good about it Bitcoin is king and ETH is nex to it and so if 5 years has passed still nothing will make them move from different rankings or will them into another phasing of cryptocurrencies. I love these two coins especially bitcoin.