Ethereum, being the world's second largest cryptocurrency by market cap, has all the potential of replacing Bitcoin in the future. It's more than just a cryptocurrency, being a platform for the development and execution of smart contracts (aka dApps). With ETH, it's possible to launch alternative cryptocurrencies without the need to start a Blockchain from scratch. It's also possible to use the ETH blockchain for other purposes such as voting, proof of identity, verification of documents, and more. In contrast, Bitcoin's only use is for finance where it cannot be implemented in other areas by its own.
Given all of the benefits Ethereum provides on top of Bitcoin, it makes me wonder whenever it'll be able to replace the pioneer cryptocurrency within the future? As long as, Ethereum keeps progressing in development and mainstream acceptance, it'll be much closer to Bitcoin every step of the way. What are your thoughts?

I haven't thought of it because Bitcoin is mother of all currencies even if Ethereum is in the 2nd position that will likely to replace Bitcoin someday. So if Bitcoin will be replace, I am sure that this will be a big news and will likely to create a fuss around the crypto society.
But if the big whales out there will boycott the support of bitcoin and they will convert to Ethereum then the possibility that it will happen is pretty big. Ethereum will likely to need 160,000,000,000$ market capital to overtake the king of crypto currencies.