Joseph:
your suggestion of men in back has no legal distinction (in secular law) from women in back.
No legal distinction, but a big practical distinction. When’s the last time you saw a video of a man making a scene about separate seating? It’s always the women complaining.
IMHO, this is due to the current national pastime of being offended by identity politics. The liberal/MSM world has instilled most of us with the tendency to view certain groups as oppressors and certain groups as oppressed, regardless of the actual facts on the ground. (If an academic comes out with a study suggesting police end up arresting more black people than white people, they’re hailed as a hero for standing up for the oppressed; if somebody points out that this because more black people commit crimes than white people, they’re derided as a racist sticking up for the oppressor.)
Therefore, liberal women have a tendency to view every separation of the genders as an affront to their being, while the men don’t. But if you put the men in the back and the women in the front, libs will see it as sticking up for the poor oppressed women, not sticking up for the evil oppressive men.
If the mehadrin buses called it something catchy in PC-jargon like “a dignity tax on male privilege “, they might even start a cult following.