I don't think so : an altcoin, whatever his technology may be will never defeat Bitcoin, because to elect the best crypto-currency, we look at how many people use it. No altcoin will ever surpass Bitcoin because the average people absolutely don't care about the internal problems, and I do not see any internal problem as of today. The branding is whatever matters the most, and good luck defeating Bitcoin's branding ! Most of the people that know some economical things knew about Bitcoin, but absolutely none about things like Ethereum or Litecoin. Good luck releasing something that beats Bitcoin on all the points, which is basically impossible if you conduct an IPO or an ICO.
I disagree. If someone comes up with an actual solution that delivers the same levels of army grade encryption and protection against quantum attacks like bitcoin does now, while being able to send fast onchain transactions for cheap at visa level volumes... that would be something a lot of people if not everyone involved in BTC would buy at. BTC will always have the first mover advantage, no coin can survive as long as BTC because it was the first, but if at least on paper, a coin solves BTC problems, its going to get a lot of money, if in practice it works its yet to be seen.
Thing is, I doubt a bitcoin killer actually exists, but i will remain skeptical.