The only way an altcoin can replace bitcoin is to find a scaling proposition that cannot be applied to bitcoin blockchain (else bitcoin developers can use the new tech) without compromising securty and centralization. We don't have anything like that right now.
So this means blockchain tech is a dead end when it comes to being a GLOBAL player. It still has its functions in smaller communities, but on a large scale, it simply cannot function as a currency being used for small to large goods?