People regularly prophecy the doom of Bitcoin. It'll be outlawed, something else bigger or better will come along, there will be a major flaw found, people will just get bored and move on.
This reminds me a lot of the early days of Magic the Gathering. It was 1995, and I had just gotten into Magic, which was a couple years old at that point. The over-powered cards from early sets were already hitting $100 each, and it seemed like newbies would never stand a chance playing against the old guard who got in on the ground floor, unless you were willing to shell out a ton of money. The game had a lot of confusing rules that were not very intuitive unless you were a hardcore rules nerd. Obviously not something that looked like it would last for long, right?
Word got out that people were dropping hundreds of dollars at a time on this thing called a collectible card game, and so competitors came out of the woodwork. Spellfire, Jyhad, Wyvern, Star Trek.... all came out and all failed more or less spectacularly within a few years. And yet Magic the Gathering is still being produced and sold, 20 years later. It's still the collectible card game. Why? What makes Magic so special, so long lasting? Why couldn't any of those other games compete? Because they weren't Magic. Just as other cryptocurrencies aren't Bitcoin.
Magic had the first mover advantage. It set up a base of players willing to spend all their allowance every week on packs of cards. It defined what a collectible card game is. By the time the other games came along, Magic was 2-3 years into its production. There was a history to the game, a depth of play in the cards available that a new game couldn't compete with.
Bitcoin has the same advantages. It defined what a cryptocurrency is. It has a history twice as long as any other cryptocurrency. When someone says cryptocurrency, you know they're trying to be polite, but what they really mean is "Bitcoin and all the rest".
This brings us to the second way Magic won: the network effect. Everyone had heard of Magic, or, if not, upon entering a gaming store, it was the game everyone was playing. You could buy cards from other games, but you'd be lucky to find anyone who'd even bought any of those, let alone anyone heavily invested and wanting to play/trade. If you chose Magic, you could interact with nearly everyone in the store.
The network effect is the huge win for Bitcoin. Go online and look for stores that accept Bitcoin. Now look for brick and mortar stores that accept Bitcoin. There's a map for that. Now try to even find a listing of places that accept coins that aren't bitcoin. Which currency would you rather use, the one that can actually buy things, or the one with the cute mascot? The network effect makes Bitcoin the Facebook of cryptocurrencies. There may be a few alternatives that don't die off, but they'll be far and away less used.
The final way that Magic beat the competition is through constant improvement. When Magic was first introduced, the rules were incredibly over-complicated. Ask any old player about damage prevention bubbles and interrupt windows. You needed a flowchart and a spreadsheet and a PhD just to figure out how some relatively simple spells worked. Luckily, the rules did not have to be static. They were constantly updated. Interactions were clarified, rules were simplified, and the game was made much easier to play and understand by even casual players.
This is a critical point that nearly all the critics of Bitcoin overlook. Bitcoin is not set in stone. Bitcoin is software, and software can be modified. There is almost no conceivable bug that could be found in Bitcoin that would actually take down the currency entirely. SHA256 turns out to be backdoored by the NSA? It can change to something else. Default .0001 btc transaction fee turns out to be too high once Bitcoin hits $100,000? No big deal, it can be changed. Bitcoin, unlike pretty much every other cryptocurrency out there, has actual developers being paid actual money to work on the software. Any problem encountered can be overcome.
So, Magic the Gathering, 20 years later. Still around, still arguably the best trading card game in existence. This despite the explosion of German style board games, video games, and the internet. Would someone from 1993 recognize the game? Certainly. Would they be able to pick up current cards and play? With a tiny bit of help, probably.
Bitcoin in 20 years will be much the same. It might look a little different. It might act a little different. But, the basic idea and workings will be the same. It'll just be more streamlined and a lot more prevalent in common society. And people will barely remember that there used to a bevvy of altcoins trying to jump on the bandwagon. Will one or two survive, the way Pokemon did, by chiseling out a niche that wasn't covered by the original? Probably. But there will still only be one original, biggest, best game in town, and that'll be Bitcoin.