There no successful coins other than bitcoin. The second largest coin is 5% of bitcoin's market cap. The third largest is 1%. It gets rapidly worse from there.
If there is ever a successful coin other than bitcoin (unclear, but maybe) it will take new approaches, not anything like any of the current alts.
Personally I don't believe hash algorithm even matters very much. By focusing on that you are getting distracted from anything that does (or at least might) matter.
You are the one that does not understand the big picture. Why was Dogecoin successful at all and has beaten Bitcoin in daily transactions several times? The answer is
market penetration.
A currency is useless without high market penetration. Guess what algos give the highest market penetration? GPU.
When people try to CPU mine and earn 1 penny a day due to botnets, most people cease to bother doing so, and the coin dies.
The future of PoW is Myriadcoin style coins where you can mine with anything and receive some kind of reward.
No. The second biggest cryptocurrency is Liteoin. I CPU mined Litecoin for months. It was a CPU coin at generation and was flooded with botnets and large computing clusters early on. The coin succeeded despite this, because eventually a GPU algo came out. I'm sure we'll see the same thing for the cryptonote hashing algo.
Myriadcoin introduces vulnerability when miners hop between difficulties and the difficulty of one hashing algo for GPU goes down and another goes up. It's not a proper solution. We saw a similar thing with RUCoin (which had SHA256 and scrypt) and the coin failed.
You seem to forget what the function of this is: money. As long as people find the privacy afforded to be favourable, it will have a usage and monetary value. This is the whole point.