[Mister_X]

If I'm understanding what you're getting at, I believe all the main dating sites already share user profiles between themselves to flesh out their "stock" of potential paying customers.

So using a specialty site like Kayak Dating, or some such, owned by this dating site group would still get you some non kayaker profiles.

I discovered this because I like round women and I'd have profiles on a few specialty sites, and I'd still get thin women profiles occasionally because other qualifiers I'd listed were close to theirs.