[vayup]

You are absolutely right that it is easy to rule out obviously bad choices, such as 3 of 3. However, determining the actual quorum to use is a qualitative risk analysis exercise.

Considering that this is an election for a professional organization with thousands of members, I am going to go out on a limb and say that it should be easily possible to assemble a group of 5 people that the community/board trusts woudn't largely collude to break their privacy. If I were in the room, I would have advocated for 3 of 5 quorum.

But the lifecycle of the key is only a few months. That limits the availability risk a little bit, so I can be convinced to support a 2 of 3 quorum, if others feel strongly that the incremental privacy risk introduced by 3 of 5 quorum is unacceptable.