I suppose it's based on your meaning of the word 'niche.' It's hardly unexplored territory - Araki being the most obvious example. Newton did a little, but his was more 'tied restraints' than actual, practiced rope work. To give you an idea, I'm not even into rope work and I have I think three books in my library from different photographers that feature some of those images. They style of tying is very different from what you have in your port, but I don't think that makes any difference to someone that isn't already familiar with the subject - even educated people will generally see different rope work as the same thing if they're not into it.
But it's not a common style, no. So you're not the first to shoot something like this - not by a long shot. But there's still lots and lots of room for you to put your own spin on it, and do it in a unique way.
Even though I've got a few books of it, I can't remember a single image offhand that wasn't overtly sexual or tongue-in-cheek. It may be an existing niche, but everyone is treating it like a niche, and nobody seems to be digging past the obvious surface of it. So if you do your homework and figure out how you can crack that and be different, there's the potential for you to make some really great images.
And if you do that, I'd be really curious to see them.