RE: Vitalik's 7 questions
I disagree with your first point. If you have 51%, you can do various attacks that won't crash the price(which actually may not matter if you are in for the long term). This is why I like dPOS where the control is in 21 actors. In Bitcoin and Ethereum, 5 pools basically decide everything.
As an example of attacks, you could target other miners: build your own fork but include all the transactions from other forks. This means that you are not going for the double-spending attack (which is not my favourite attack actually) but you are going for the mining rewards. Users are inconvenienced but they don't loose money.
For the whole cryptospace, the N°2 should be the most concerning. With all the money and people involved, did we achieve anything? I do believe that cryptocurrencies and blockchain are not just a technology but more of a movement. For me the success is not to replace everything with cryptocurrency, blockchains, token, decentralization... The success will be to put pressure on centralized systems, so that they give back more power to users or rethink their models.