I think it's fairly obvious that, at the very least, this won't be the next trend. Female superhero lead movies aren't doing as well as male leads, and people still mock wuss men characters in movies. Further, movies and books that push this are usually banned in China, which is a big market. It'd take a massive shift in perception in the world, and I don't think that'll happen in the next 3-5 years. We've been in the falling action of isekai as a genre for about 2 years now, so we're just waiting to see what single or plural series end up selling like hot cakes that ends up driving the new genre, and I don't see any evidence that gender bender series are doing well enough to actually drive a wider trend.
I stand by (given Frieren is now the highest rated anime of all time, and has held the title for a year) that we're already probably in the transition phase. Maybe it won't be Frieren style series, but that's really the only big thing in recent times that I can think of that would be a driver for a bunch of new series, but it also didn't have quite as much of a reach as I'd expect for it to do that.
I actually think there is a much higher chance of a backlash, super manly, 1950's style masculinity being the next trend over effeminated males being the next trend.