great insight on what 51% attack will do to blockchains. This is happening a lot lately to new and low overall hashrates of many coins. Electroneum is a good example where someone or group buys a massive amount of hashrate for a short term to interrupt the overall blockchain. Either making it stuck at a specific block or ruining the pow of the coin. I think their incentive of doing this is so they can get more of the coins initially before the coin hashrate explodes as more people get involved.