Bitcoin has already gain popularity therefore it is hard to replace it by new currency, the volume is already big and we are seeing now is the exchanges that accepts bitcoin only.
Being the first mover in the markets, it has many advantages over other cryptocurrencies whatsoever. Of course, it's behind other alts which have better speeds and cheaper fees, but up to date, it's the strongest cryptocurrency in existence. Among many people, Bitcoin is digital gold. It would be nearly impossible for any cryptocurrency to replace it, unless it comes with a better technology which address all the underlying issues within the pioneer cryptocurrency.
Every day, Bitcoin grows in user adoption and acceptance worldwide. Therefore, the more it grows, the harder it will be for any other cryptocurrency to overcome it in terms of market cap and popularity. The closest one to overcoming Bitcoin is Ethereum but it might replace Bitcoin as its supply is limited which gives it inflation over the long term.
Nevertheless, Bitcoin is the original cryptocurrency which has brought us the basis of blockchain technology. Every other cryptocurrency is also based on blockchain technology, so that makes them copies of Bitcoin which can never replace it in the future. Just my opinion