Since 1179 (and with a few very minor exceptions in the centuries right after then -- none since 1612), the Catholic Church requires a super-majority of 2/3 to elect a new Pope. I don't see how the choice of a BDFL is so much more important to the Python community, than the choice of a Pope is to the Catholic Church; thus, requiring 90% rather than "just" 2/3 seems unwarranted.
In fact, a 90% requirement gets dangerously close to a requirement for unanimity -- allowing any member of the Sejm to shout "Nie pozwalam!" and thus end the session and nullify every decision made in the session. As
https://en.wikipedia.org/wiki/Liberum_veto puts it, "Many historians hold that the liberum veto was a major cause of the deterioration of the Commonwealth political system" all the way to the partitions of Poland.
Let's steer well clear of this: those who cannot remember the past, etc, etc...
Alex