BTC Endgame
You don't need a DoS attack under the assumptions of this project.  It's already assumed that you control ~80% of hash rate, so you execute a 51% attack that mass double-spends coins and destroy all confidence in the integrity of the currency.  Poof, nobody uses it.Note that China already controls ~65% of Bitcoin hash rate, so if they wanted to execute this right now, they probably could.That they haven't is one reason I'm bullish on cryptocurrency, and specifically Ethereum and Stellar, and it's entirely separate from why many other Bitcoin bulls are bullish on cryptocurrency.  You don't need proof-of-work to secure a blockchain.  You only need game theory: as long as each participant has more to gain from allowing Bitcoin's continued existence than destroying it (and they can't subvert or destroy it in a way that will be invisible to other market participants), it will continue to exist.  China gains no benefit from destroying Bitcoin; they can just continue to let it exist and tax all the Bitcoin miners in China, generating revenue for themselves and their citizens and continuing to be a thorn in the side of dollar hegemony.This also implies that proof-of-stake (if done right) is just as good as proof-of-work, which'll solve the energy issues associated with Bitcoin.  And it means that cryptocurrency adoption, if it happens, isn't going to be because it's particularly good: rather, it'll be because the U.S. has destroyed the dollar.  There's value in cryptocurrency simply in it being an alternative that's readily available, so that civilization doesn't stop if the U.S. does end up miscalculating and hyperinflating the dollar.