Nothing.
Discovering that one woman shares a favourite colour, lipstick, voting preference, musical genre, opinion on marmite with one person of the opposite sex is not of any life importance, and doesn't create a universal common 'woman' group which excludes all men and includes all women.
There is NO commonality between 'transwomen' and women other than three consonants and two vowels, which is why there is such vicious fighting so hard over the words for female humans. Gain the rights to the female words; dissolve the rights of the female people to use it to distinguish themselves from you.
There's literally nothing else, no substance, no commonality, nothing. Nothing shared that groups women and transwomen into a meaningful group and distinguishes that group from men.
There's humans, a group to which all of us belong.
Then there's female humans / male humans; two groups starkly different in the human race. All female humans are the opposite sex to all male humans.
Where sex is relevant, all humans are irrevocably one of the two. The same as one half, different to the other half.
There are profoundly compelling reasons for recognising the two classes. The impact of sex upon life is stark.
There is no reason whatsoever, to dissolve recognition of that gobsmackingly real and profound distinction that nature sorts us all onto one side of or the other, and to replace the sorting of all humans into two incomprehensible groups based upon what?
One female human once had a nice chat with one male human so he's now the same class as 3.8 billion other female humans? We've decided the official life classification should be people we haven't had nice chats with/people we have?
Or people that have ever worn flappy fabric around their legs vs people who wear tubular fabric encasing each leg?
Or people who've been beaten up by some humans vs...what, people who haven't?
If you dissolve the sex distinction then there is no male violence to talk of. Just indistinct human violence.
The sex distinction is real, meaningful, and has affected every human living or dead. It persists whether we pretend not to recognise it, or are honest and acknowledge it.
There is no replacement categorisation that makes any sense, and is universal. You can't replace sex with a nonsense human division.
We're all humans.
Half of us are female humans.
The other half are not.
There is no way to force yourself from one group into the other without simply dissolving the right to recognise the reality thats shouting in our faces.