The real question is whether workplaces will understand and respect the law.
I think it's becoming pretty clear to everyone that you cannot label a space "women" and exclude men from it if you are allowing trans women to use it.
Unfortunately I think some organisations will simply relabel women's spaces unisex, believing that this has resolved the problem. It will take more litigation to establish that where you have traditional single sex toilets with gaps over and above the doors and shared wash basins, these are not suitable to be repurposed as unisex toilets as they do not provide sufficient privacy.
Once it becomes clear that unisex toilets need to be fully enclosed rooms with wash basins, organisations will have to decide whether they are willing to rip out perfectly serviceable single sex toilets and replace them with fully enclosed individual toilets, which will reduce the overall toilet provision as you cannot have the same number of toilets per square metre of floor space. At this stage in the game I think some organisations will abandon the idea of unisex toilets and quietly direct trans people towards accessible toilets instead. (Which may cause problems for disabled people if the accessible toilet provision is not sufficient for the number of disabled people using the facilities.)
Some organisations will seek to demonstrate their commitment to trans people by retrofitting their facilities to make everything unisex. They will then discover that there are certain disadvantages to this. The Barbican are about to discover that people needing to use the toilet during a fifteen minute interval are not thrilled about longer queues due to a reduced number of toilets, and that there is a consequent loss of revenue caused by people buying fewer drinks at the bar and, ultimately, fewer tickets to events. Some other organisations are also likely to notice drops in profitability or productivity caused by people spending more time queueing for the reduced toilet provision and less time spending their money or making money for the business. I would also expect them to have to deal with an increased number of complaints about safety and cleanliness. They are likely to come to the conclusion that they should have just accepted that trans people would be pissed off, rather than pissing everyone off to accommodate trans people (who will still not be happy).