To be honest, I don't think there will ever be an alt-coin which replaces BTC or is better than BTC. bitcoin already has everything needed for mass adoption. does the normal user need anon transactions to pay for his coffee? I don't think so. there is not even a #2 crypto coin beside BTC, since it is just not needed. there are successfull alt-coins (and unsuccessfull ones). They all share the same pool of money, and they have to fight for their part of the pot. and for them new features are important. no innovation? no evolution? you'll get behind.
you can earn some really nice money with those alt-coins, but do you really think even one of them would replace btc? I doubt that...and it doesn't matter if the coin is doge, ltc, drk or whatever (well, to be honest I was even able to buy something with doge before, which makes it the only alt-coin so far for me with real value). In the end they are all the same, just alt-coins. the good ones which are able to attract investors will make it at least until the new fotm is there.
Bitcoin will not be used to buy coffee, except in a few geeky cafes.
First of all, it's not scalable for that.
Second, why would the public exchange their fiat to bitcoin just to spend it on coffee if they could buy coffee with fiat more conveniently in the first place.
There are over a million or two million used addresses in Bitcoin, but real people behind them are an order of magnitude less, so roughly between 100 000 and 200 000 users of Bitcoin, with 90%+ of all bitcoins used as a new way to store money away from the banks where money can get a bail-in and as a speculation vehicle. Most people who think Bitcoin is becoming something of a mainstream are just dreaming. This is not the case, Bitcoin is a mosquito vs an elephant of the financial industry.
Will Bitcoin retain its function as a relatively good (if you buy at the right time) store of value? We shall see in the coming months and years. But it's not designed for everyday transactions, that one is certain. Litecoin, being just a clone of Bitcoin, is not designed for that either. And, as we can see, Litecoin has been a terrible store of value, as it lost 80% since its peak.