I suspect Open will be extremely unpopular or devalued as a category, but it’s sensible to have it.
it’ll effectively function as (and be perceived as) a second tier men’s category. One where anyone can have a go, but everyone knows the real prestige is in the Mens category.
The risk is it becomes a place for people who didn’t quite qualify for the Mens to access competitions anyway. If adopted at grassroots level, Open may end up full of men and boys who are just short of a qualifying time and need a chance to swim
at a particular level to try to get one, or to go to the (for example) nationals when them missed the QT for the mens. So a less prestigious men division 2 category. But where you might find yourself swimming against the odd woman or transperson.
I expect it will turn out to be quite hard to set QTs for the Open category.
And it’s likely that many trans women don’t want to swim in Open anyway. Or Mens. They want their identity validated (and the biological advantage) to be gained from being in the Women category.