I guess this fetish is related to anticipation. So the thing that gets you off is the part of your brain that loves the build up and the waiting (that is if you're the one being teased). If you're the teaser, you must get off on the ability to bring someone so close, yet not send them over - and that's a skill (as well as a nasty streak if you use it too often with a partner who doesn't get off on that!).
There's a real thrill with anticipation - that build up of adrenalin that makes you wonder if you're a flight or fight person but no matter which you are, your body is primed and ready for it. It leaves you breathless, wanting, giddy, excited, and waiting. It's a heady feeling - like that feeling of falling in love - and nothing else in the world matters except that feeling, that waiting. You're focus is so intense.
As the person watching, and causing this, it must be a thrill ride in itself, kind of like being a maestro of playing an instrument. You have the person so finely tuned and you know exactly how each chord will sound and strike, that you can play to the crescendo but never tip that over. That's masterful. Which is why I think this is so often used in D/s relationships - it is masterful and therefore perfect dominant play.
To orchestrate this well, you'd have to know the person, or be extremely good at reading people's signs and body language. You have no real margin for error because once you've gone too far with an orgasm, it can't be stopped.
I like this is idea, not only for a fetish but as an aspect to a relationship. The brain is such an important part of sex, and to be able to play with it so your anticipation is on a knife-edge is very very arousing. This is definitely appearing in the book...but I'm not quite sure how yet! I think maybe it will be something that someone does subconsciously at first until they realise how 'good' they are at teasing. It might thread through the whole story. Who knows...but it's fun thinking about it :)