thoughts re: a/b/o, I’ll disclaim this by saying I don’t know the ‘fandom history’ of a/b/o, I just know what I know about it from reading a/b/o in tw fandom, so my perception may be skewed and I may not have all the information, but. I have thoughts so, away we go --
we’re obviously talking about a trope that is, by design, an excuse for men’s* bodies to function similarly to people with vaginas in that they self-lubricate and are able to get pregnant. my assumption has always been that it came to be without recognizing that there are trans men and masc-aligned nb people whose bodies... do those things. obviously, this assumption is based off the fact that trans people are rarely, if ever, thought about in fandom or considered during fandom discussions.
*characters or people seen/assumed to be men
a/b/o could be an interesting discussion on gender roles -- here you’ve pretty much constructed a world automatically divorces gender from sex -- everyone in this ‘verse has a gender identity + a, b, or o. a/b/o determining whether or not they are able to get pregnant/impregnate, as opposed to this being a cissexist assumption people make based off gender identity/assignment/presentation etc like they do irl.
due to the nature of fandom, I have no idea what a cis female’s role in a/b/o is -- whether or not they’re infertile unless they’re omegas, if they’re able to be alphas despite being unable to impregnate people, or if a/b/o is only relevant to cis males -- here I’m assuming it depends on the person writing it.
in playing with gender roles you could say: no matter what gender they are alphas are capable of impregnation and have strong care urges and etc. -- so if a cis female is an alpha, she has all the parts necessary to impregnate, i.e. a penis and a knot. betas are? traditional cis bodies? which is actually great commentary considering betas are essentially ignored in a/b/o fic therefore cis gender roles are ignored and unimportant to the world, therefore cissexism could very much not exist. and omegas, no matter what their gender, are able to be impregnated.
(since many cis male omegas have penises and a self-lubricating entrances, all omegas could have those body parts. but this in combination with alphas also having penises, prioritizes body types -- especially cis male bodies, since this is fandom -- with penises over anything else and well, that’s old hat and shitty imo.)
since I know many creators who are trans or cis, and do consider gender when writing, I’ve read a handful of fics that are o/o or have transfem alphas or address the cissexist flaws in a/o dynamics, but this is not the traditional fandom route. a/b/o is rarely used as gender commentary. it’s usually used in kink, so what it boils down to is... fandom constructing an entire trope that essentially ignores trans men and masc-aligned nb people by giving cis male bodies the ability to be impregnated and self-lubricate while simultaneously reinforcing heteronormative gender roles through the a/o dynamic.
and that is why I see a/b/o as inherently transphobic. like I said, I’ve written/consumed/enjoyed a/b/o, but I think it’s important to recognize the ideology that a lot of it reinforces.