There cannot be a next Bitcoin and the paradox of replacing a store-of-value (SoV) applies. Any successful replacement of BTC will forever undermine the credibility of any successor.
bitcoin is not a store of value, bitcoin is FIRST a CURRENCY and then because of a dozen reasons it can be used as a store of value.
and there can be "next bitcoin" but it doesn't have to replace bitcoin! it is like saying there could only be room for only one CPU (Intel) and there is no room for another one (AMD).
if some day a better innovative idea came along that could be as good as bitcoin, it will simply grow to bitcoin levels and is used alongside of it.
Medium of exchange(MoE) aside, I cant think of another legitimate use case for decentralisation. At a stretch illegal marketplaces may benefit from decentralisation given the risk of censorship or seizure of assets.
not everything is about illegal activities. most of the times it is about not wanting to bend over to the corrupted centralized power. look at India for instance.
It is obvious that where BTC goes all the altcoins follow anyway, just have to pare this down from these last 4 altcoins hoards of any note.
well, i don't know how obvious it is because i can not find any altcoin at all that has followed bitcoin over the past 22 months! over that period altcoins have constantly gone down while bitcoin had its fall and then has been rising for the past 10 months.
for example bitcoin dropped ~80% and after reaching bottom in Dec 2018 it started rising a couple of months later and has gone up 250% in total
litecoin has dropped ~80% and after reaching the bottom Dec 2018 it had a little dead cat bounce where it goes back up for some time and then comes back down again to the same bottom it reached in 2018!