Problem is that there are heaps of tube sites now as well.
Pure filth probably converts the best if it's a fetish and the stuff isn't being mass produced by the porn industry. A product is even better; here's an example.
Dakimakura or Japanese
love pillows (Please don't ask how I know about these!)
I don't know if there are rules about redirecting a .com.au to a .com but provided it isn't highly illegal, I doubt they'd ever bother you.
You could always register it and toss up hand written reviews of all the paid membership sites in that niche. If it's available to hand register, I'd probably pay the reg fee at least.