Even if a new alt-coin emerged that was vastly superior to bitcoin in EVERY SINGLE ONE of its original goals, joe-public, investors and many service providers would probably feel no massive urge to switch.
If the altcoin has sufficient demand (not even any where near Bitcoin) to generate a liquid exchange, then the altcoin can be converted on the fly to pay those who accept only Bitcoin.
So an altcoin doesn't need ANYONE to switch from Bitcoin, it only needs to grab a small percent of the market of new users. Bitcoin only has 350,000 users. There is a long way to go to 7 billion.
The key though is the altcoin needs to present something truly useful that Bitcoin can't copy. So it has staying power.Agreed.
I think the bold statement is the main reason why todays serious altcoins are here to stay (and justify a rise vs BTC)
The consenus required to do a hardfork is impossible to reach for anything other than fixing threating security problems for anything that actually changes someting. POS is unreachable for bitcoin and a true improvement over it. For everything else there would be an oposition against it and so prevents innovation on BTC itself.
People tend to forget that there is a difference between innvation on crypto and innovation on bitcoin. It doesn't matter that something was initially written for bitcoin since it can't be bitcoin exclusively. Bitcoin can't keep her innovation for itself, but also can't grap new innovation from the other cryptos.
The first crypto to buy is bitcoin, but some of the newcomers might see a feature, I think it will be POS and especially POS rewards, that is nice to have. I expect some of them to move on to altcoins, the % of is up to you, but that's basically the thing that matters.
Even if you don't belive in this there still will be a few idiots, lets say n% of them that want to become early adopters (as we are 350k/worldpop wouldn't be damm early) and they can be that rather on alts. The % is still up to you.
The massive urge to sell BTC for altcoins wouldn't come from the actual benefits for individuals from the altcoins features. It would come from possible profits and saving profits. It's always a bad idea to have all wealth in one thing, so it might be a good idea to move some % into different altcoins. Just to be save, and maby that altcoin will grow faster than bitcoin and there is no practical difference in using as payment.
A smaller crypto can easier double your wealth than a big one, so my point is about marketcapitalisation. Look up the % that all serious altcoins MC have compared to bitcoin and compare it with your estimated % on my previous points ...