Four words, three rounds
Seven is lucky, so the author made the prize 77 mBTC "to celebrate" and released the question in phases. The first one is "Four words and a period at the end." The author says it plainly: in that phase it's "close to impossible to solve". Update 1 adds "My handle name is Aoi Nakamoto." Update 2 asks the real question: "Why did I choose that handle name?"
The rest is the old recipe. Append the last three characters of the block 6 key, MQz, the ones the author printed when block 6 got stuck. SHA-256, entropy, m/44'/0'/0'/0/0.
Take the consonants out of Satoshi and you're left with a, o, i. So the answer is "Satoshi without the consonants." and the string that derives the key is Satoshi without the consonants.MQz. The period stays, and there's no space before MQz.
The post also drops a bigger hint about the whole series. The author has "one and only one purpose" for this quizchain, won't say what yet, and it needs the chain to run until block 77.
Fourteen and a half hours
Funded at 02:50:59 UTC on April 8, five minutes before the post, and claimed at 17:21:46 for 7,699,000 satoshis. The third update just says someone took it and gives the solution. Later that night one commenter wrote that they'd solved it "a bit too late", and another had tried "some variations" on "only the vowels". Close. The record says solved and names nobody.