Can I recommend Chapter 2 of Caroline Criado Perez’s Invisible Women book before you decide to try & influence anyone? A bit of background knowledge & understanding of the different needs between men & women, and why even now , women have less provision than we need, even when toilets are designed 50/50 for male/female allotted toilets.
Suggesting to any workplace that they should reduce female only provision to accommodate gender neutral is most likely going to walk them straight into the possibility of indirect discrimination against women. No matter how many women you think would be ‘cool’ about it. It only takes one women to make the case, and she’d be able to sue & win.
But again. If you think you’re knowledge on workplace regulations, equality law & EHRC guidance trumps your HR department - Good luck persuading them to reduce female only provision in favour of mostly gender neutral. 👍