Is this really such a weird story that it would get editor blocked in a regular manga?
Today, no. It absolutely could get published today. But I'd have to take you back at least seven or eight years ago, when Onimai only had one or two chapters.
For a very long time, gender bend was considered bad luck to publish. Mostly due to every time someone attempted the premise it either winds up needing to be axed (manga) or pulls abysmal ratings (anime). A lot of that was down to gender bend works at the time not really utilizing the concept to its full story potential and the purse-string holders engaging in a self-fulfilling prophecy. There was room for Ranma 1/2's success and like, nothing else practically.
That changed in 2017 with the movie "Your Name" which... it's almost impossible to adequately describe how much it was a success in Japan. While the gender subverting element is only one part of that story, it definitely threw the curse into question. It would still probably be an uphill struggle if Nekotofu wanted to publish it through official channels at the time, especially with such a twisted-sounding elevator pitch. "You see, this little sister drugs her big brother--"
Incidentally, the curse is just cinders of memory now. The Onimai anime was a smash hit, topping Nico's charts and doing gangbusters in blu-ray and merch sales. And yeah if you noticed a
huge upswing in the amount of gender bending manga and anime since 2017, that probably has something to do with it. We're probably going to get a ton more in future thanks to Onimai in 2023.
(In light of helping to significantly changing the Japanese media landscape for the better, I'm inclined to let Nekotofu enjoy his pee fetish. Most people want a golden trophy for their accomplishments. He apparently wants a golden shower.)