For cryptos to be used as an actual everyday currency I think there needs to be a third main pillar in the crypto world beyond bitcoin and ethereum (assuming they both succeed as store of value/move or spend big money and decentralized apps). A coin that fully confirms a transaction within less than 5 seconds - about how long you wait for the credit card to work in a store - and fees on the order of a cent so that small purchases and micro transactions are possible.
This is not the main issue. The main issue for a crypto to be considered a currency, is that it has a stable value ("ideal money" of Nash type). Such a crypto must have a value-regulating mechanism, and not an "amount-of-coins" regulating mechanism. If you simply know that the amount of coins that you obtained to sell a car today, will be buying you such a car 2 months from now, not 3 cars, and not half a car, you have a reliable currency. No "diminishing emission" coin can do so, because all of them are desiring "increase in value" and hence, speculation, hodling, and volatility (and end up becoming greater fool games, rather than currencies).
The confirmation time stuff is a detail compared to this. In fact, the time you need to wait for most crypto to confirm, implies already potentially a serious value fluctuation. DASH has an instant confirmation mechanism, but I'm not sure it is actually secure. It is more a kind of gentleman's agreement between master nodes and miners; after all, miners can always decide not to accept the master node confirmed transactions ; but at least, a miner doing so is modifying the protocol.
The technicalities of transaction confirmation and so on, are only second-order. The principal reason why bitcoin and most other crypto cannot become a good currency, is because they have emission curves that turns them into highly speculative assets, which a good currency isn't.
That said, speculative assets DO have a bright future (until they cause a financial crisis, which they always end up doing).