The dominance, popularity, volume and investor confidence are all relative and volatile. This can all change in cryptocurrency in a few days. As some here correctly refer to one Jewish proverb, one should not follow the crowd. Therefore, it’s best not to bet on the coin on which the majority puts, especially, only on one specific coin, no matter how promising it seems.
As for ethereum, then everything can be. Any coin can be replaced with another one in the future, bitcoin still has some immunity, however, in the long run, everything is possible.
Agree. For what I know, no crypto is safe on the market. Every cryptocurrency's place on the market, can be taken by another crypto with greater popularity and usage than it. If Ethereum becomes more actively used and traded than Bitcoin itself, there's a probability that it could "flip" the pioneer cryptocurrency someday. Technically this seems impossible since Ethereum's supply is virtually unlimited. But considering that crypto behaves in strange and bizarre ways, anything could happen. I've seen altcoins with no real use cases being pumped in price until they outpace others in terms of market cap. The same situation might happen with Ethereum as it experiences a boom in demand and adoption with its wide variety of dApps, and most of all, unparalleled scalability.
Despite this, one would prefer that both cryptocurrencies remain in the way they are right now. Ethereum does fine as the world's second-largest cryptocurrency by market cap, being a complement to Bitcoin in every way. In areas where Bitcoin cannot fulfill certain tasks, Ethereum fills the gaps. If we were to make a comparison between both cryptocurrencies, we could say that Ethereum is the "Gas" or "Oil" of crypto land, while Bitcoin is the "store of value" or "digital gold" of cyberspace. One quick shift in price, and market capitalizations could change in a blink of an eye.
Nonetheless, Ethereum replacing Bitcoin could present drastical changes to the entire crypto industry. Bitcoin's popularity will decline, while its status of reserve cryptocurrency of the market will be no more. All the eyes will shift towards Ethereum bringing a huge wave of merchants, businesses, and individuals alike while Bitcoin will be overlooked by many. But we all know, that this is very unlikely to happen in the future. Just my opinion