Also, I agree that any bathroom won't accommodate everyone. But no current bathroom does that either.
For unisex purposes it depends on the bathroom design surely.
People have this idea you have some semi-public space because people might see each other in a state of undress.
But almost all westernised bathrooms contain a bunch of toilet stalls.
If everyone is going into a toilet stall to do their business - standing or sitting - then the only shared space is for washing hands or preening in front of a mirror. And if that's an issue, optionally put that in the stall too.
If security is a problem - many toilet stalls have limited doors/walls around them - then make it secure. This effort would benefit everyone.
Then humans - whatever their persuasion - could simply do their business in peace and get on with their life.
Any bathroom wouldn't be able to accommodate everyone. For these exception there can be single cabin room or something else.
There are a lot of bathrooms for both sexes, mostly in places where space is limited. But having segregated bathrooms is in no way a problem anywhere and I think many people are happy with that.