It’s true that porn is a big part of the internet at large. You can point to countless examples where a product (even social media) lived and died by porn.
But there are also countless examples where porn was never a factor. Most of the major social platforms today have always had an anti-porn approach. It’s debatable whether that helped or hindered their growth, but it’s always been a thing.
Now, I can’t think of any where porn was a big part of their platform that got removed, and they came out ok. Maybe that’s (part of) why Reddit has been downplaying porn for a while.
Right now, there is plenty of porn in the fediverse. But there will be the same challenges as any user-submitted porn site. There’s currently a big discussion about categories that are unwanted, generally offensive, and illegal in certain jurisdictions. The fediverse makes all of that more complicated. There’s also a big concern about the content being uploaded directly, increasing the load on every instance that federates.
There will definitely be porn here, but I don’t think it’s going to work the same as it did on Reddit.