Yeah when you mention it, I did small free mature sites for a while and that converted like crazy as well.
Was using a sponsor called "In praise of Older Women" or something like that, they had exclusive content and even tho the sites design was just like any other paysite I kept getting checks for like 1½ year after I stopped working on those sites.
So yeah, focusing on rare niches should still work if ya know what you're doing ;)
I've seen some goth paysites around, that might be something, not the typical trashy all covered in make-up goth but more just the clothing, lots of corsets and latex and stuff ... that might do well with the right type of traffic, afraid I know of no such sponsor tho.
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