I believe Ryan Air in Europe was experimenting with charging to use the restrooms. They're also charging for carry ons now.
There's also talk that this is the next step for things:
Boeing is reacting to what the airlines want. I can’t criticize them.
I’m just a bit surprised the airlines haven’t started selling vouchers for in-air restroom access, with swipe access control at a higher rate.
I believe Ryan Air in Europe was experimenting with charging to use the restrooms. They're also charging for carry ons now.
There's also talk that this is the next step for things: