I think they will, if it is better.
> going to have to genuinely nail it with a currency that is instant, costs almost nothing per transaction, is very easy to use,
There are such cryptos. stellar, nano and i m sure also others. And i think monero's anonymity promise is a big selling point too
It just need to be stable enough for the length of the transaction. As long as you keep the bitcoins moving, the gain/loss will distribute itself over everyone and it won't be different than any bank fees.
Let say I want to buy something from you for 20$ USD, I'm in Canada, so I buy 27$ CAD of Bitcoin on a local exchange (so I buy it from someone that essentially just sold something), I transfer the resulting Bitcoin to you, you then sold it as soon as you can. Even if the Bitcoin price is losing 25% today, if you can do all that in 2 hours, you will only lose about 3%, which is similar to Visa fees. Ideally you wouldn't hold them for more than 5 minutes and it would all be automated behind the scene without your knowledge, probably through your bank if they move quick enough, but that could be through a third party too (which is the beauty of it all, you depends on no one).
That's an ideal world though and I feel like that's an utopia but that's how I see we can ignore the stability issue.
I think there are ways to make them less volatile. For one, don't list them in any crypto-to-crypto exchanges, instead allow only dollar cash-ins/outs, or limit the amount that can be exchanged to some fixed value like $100 / hour. Speculation and greed is limiting the prospects of most coins.
Stellar is trying to achieve a completely different goal than exchanging stellars coins.
Almost no one of those crypto could achieve even half of the current daily transaction processed by CC, and the proof they are using is in no way as safe as proof of work, even if more efficient. Why would people adopt them? There's no advantages, fees would be similar probably