Eschaton

The vision or even addiction to having the human male shell coom on the human female shell is really common.

So when we learned about Star Control and the coins were flipped there was much chagrin. So in the alternative thought, there are many different avenues to deciding who should get the male shell and who should get the female shell. The major ones I know about are:

Birth Right - Obvious. But many are born genderless
Gravity - But what is the chosen point of gravity?
The Demonic Right - The Nephilim have the right to that shell
Overmale - The people of this realm have the right to that shell (because of the infinite personal wells)
Parsimony - Those who choose evil over good have the right to that shell (not as simple as it sounds)
The Game (you just entered it) - It's a personal, on the spot decision

I favor a mixed approach, with all things including the flip plus position in society taken into account.