Adapt or die.
I knew a random Moneroer would show up eventually. It's possible Monero or Zcash will occupy some type of niche market, but the anon wars of incrementalism would have to end first, and I'm not really seeing how that's going to happen. You would need to subscribe to four ideas for Monero to really do something:
1) Smooth's claim that currency is the killer app of the blockchain (likely plausible)
2) Anonymity is a mandatory feature set of that app (less plausible)
3) Governments would not make the anon currency extremely difficult to use while allowing BTC instead, crippling the anon currency market cap
4) The need to believe on-chain anonymity would be useful in a clearing/settlement network.
If your key feature is not utilized in the likely evolution of the network, you're relegated back to the niche market. That niche market could be worth billions of dollars though, so I guess it's all relative. BTC on the other hand could go to trillions as a settlement layer. There's just not an overwhelming need to make Bitcoin obsolete and switch when both coins operate roughly the same in the end game. Ring signatures will likely block many further on-chain scaling options to boot.
Why is your argument that cryptocurrency can't survive without Bitcoin, "Monero is a niche coin."? (and that's paraphrasing for the rare literalist who will assume I'm making a direct quotation when reading the quoted material above would lead most sophisticated readers to realize that it was paraphrasing).
When I got into cryptocurrency, there was a belief that Bitcoin was anonymous enough and Bitcoin held mid-90% of total cryptocurrency market cap--I'm not saying the two are related BTW, just issuing two facts of the time. Today Bitcoin accounts for low-70% of total cryptocurrency market cap and the Evolution/BTC-e fiasco showed that Bitcoin was not anonymous enough (at least not enough to avoid taint).
My point about stocks is that no one company is big enough to rule the stock market anymore than any one cryptocurrency is big enough to rule cryptocurrency. Bitcoin has some stupendous flaws, and if unproven Eth can get to 1 billion, an actual fungible currency can get to 1 billion.
I'm not against Bitcoin, but listening to Bitcoin supremacist angle and rail against altcoins as if Bitcoin was sacrosanct and untouchable, is to say the least, a bit much. Especially considering that Bitcoin may prove the niche coin (a kind of digital gold perhaps) and the discovery period of cryptocurrency may end with a coin (or maybe more) with substantial marketcaps larger than the coin that was first, but not so adaptable, and certainly not the limitless in its potential.
My guess is that while Eth, XMR, and other coins get auditioned by the market, we will see an even greater shift in the marketcap than the one that took place over the last year. Would it be that surprising if Bitcoin's market cap was in the ten of billions five years from now, but held less than 20% of the overall market cap? Maybe, but I would have never though it would be below 80% a year ago.