Stunning read, decentralization works in the best interest of hive and I liked how you highlighted the possibilities of how the chain can be controlled. Firstly exchanging partaking in blockchain governance has experienced it's own notoreity, I think I remember houbi and binance helping Justin Sun to do the same thing. They we're in the news for so long and this exactly brings distrust and bad publicity, so I think this might make exchanges think twice with helping rich entities to take over a blockchain. The whole cryptoverse thrives in trust. When trust and track record is breached, business is bad especially for exchanges, but then, they can do this if the money is too much to refuse. 
In reality, 40 accounts owning 50% of hive seems alarming on the surface, but I doubt if these 40 accounts can align to take over the Chain. It would take some great length of Sabotage. 
As per the 30 days cooling period, this measure is also great. I guess hive has taken a lot of preventive measures.
Nevertheless delegated proof of brain is still an issue especially when it comes to distribution. 
However, we're forked and more decentralized than steemit and steem ever was. It's probably a work in progress.

@tipu curate