It might happen someday, people used to think Myspace was the best and then Facebook overtook it. Bitcoin has become super dominant but so have many other companies in the past and then they end up losing market share. Also don't forget that bitcoin had a couple inflation bugs in the past.
That's certainly true, mate. The same way Facebook replaced Myspace, the same situation could happen within crypto land. Bitcoin has been the most prominent cryptocurrency for a very long time, yet being extremely limited in transaction capacity. There are now several altcoins with greater scalability and features which prove to be tempting towards people in the mainstream world. With their superior design, they could take down Bitcoin at any point in time. While this is true, most altcoins (if not all) lack the most important thing for long-term success. And that is mainstream adoption.
In this regard, Bitcoin is still in the lead with first-mover advantage within the crypto market. It'll be quite difficult to take down its place as the world's largest crypto by market cap, because of its strong branding and mainstream recognition. Not even Ethereum has been capable of overcoming Bitcoin, despite being superior in every way. Every day, Bitcoin's market cap increases by a large margin greatly minimizing altcoin's chances of surpassing the pioneer cryptocurrency within the future. If you take a good look at today's market, you'll notice that ETH's market cap is far behind Bitcoin's. Which is why, I believe that no altcoin will be able to replace Bitcoin in the near future.
Nonetheless, the only way an altcoin could replace Bitcoin is if the same gains massive traction within the mainstream world. It needs proper marketing/promotion, and mainstream usage in other to establish itself as a true contender of Bitcoin. Even so, it would need to prove its security and stability as a cryptocurrency for daily transactions that's proven to be better than Bitcoin itself. Considering that most altcoins are efficient but not as secure as Bitcoin is, it'll take a long time before we'll be able to experience a true contender that will challenge Bitcoin's place as the world's largest cryptocurrency by market cap. Just my opinion