Two broader thoughts that have come up in discussions elsewhere.
1.) Luke-Jr stated the other day that he foresees ring signature functionality being implemented into Bitcoin in 2-3 years. My response was that even if that actually happens, it wouldn't have a mandatory mix-in level, limiting the anonymity capabilities that Bitcoin could offer with it. However, I've heard others state that you actually wouldn't need a mandatory mix-in level for it to impart "good enough" anonymity for it to kill interest in anything else. Regardless of whether this is true or not, it does sound like something that could steal some remaining thunder from the anonymity-niche coins, given that Bitcoin already has a huge market share.
Unfortunately, I don't know enough about the code or cryptography, but my thoughts on this are always related to network consensus (and this was mentioned somewhere else in the threads). There's enough fanfare currently over increasing blocksize - I can't imagine the hurdle faced if the network wants to switch to a core that introduced privacy. I've seen a couple shocking posts by "legendary" members that are essentially "we don't need a private blockchain".
2.) I've had discussions recently with Bitcoin maximalists who claim that anything built on an altchain cannot succeed, because Bitcoin's blockchain will remain by far the longest chain, and any other altcoin based on a PoW altchain that *ever* begins to compete with Bitcoin for market share will cause interested parties to attack it with the magnitudes of greater resources that are behind the Bitcoin network. My thought on this was that given that Monero uses a different hashing algorithm than Bitcoin, the resources behind Bitcoin couldn't be redirected at Monero in any direct sense (especially if the predominant resources behind Bitcoin are ASICs). Now, that isn't to say that there couldn't *still* be enough incentive involved, if Monero ever became more popular, for Bitcoin supporters to attack Monero by devoting fresh resources/energy to attack it. Thoughts?
Regarding the possibilities that bitcoin network operators would attack the monero network by investing resources in either 1) server farms or 2) GPU farms or 3) ASIC development with the explicit purpose of network destabilization: this would require a lot of resources, assuming that at this point monero has grown to the point that it "threatens" the bitcoin network "market share". This would probably require much coordination of the bitcoin network operators.
if it comes to this, IMO, bitcoin has already lost the war in the fight for a decentralized value transfer system. If the above scenario comes to pass, it means that all that bitcoin has done is transfer the power from one set of entrenched elites to another set of entrenched elites. (May the people be always in their good favor.), and the bitcoin network will continue to have to play whackamole.
but enough of this future speak. we're in the now. be here now.