I think for some couples this approach would work, but everyone would have to be pretty outgoing. I would be fine with this if someone came up and proposed this, but we'd never get any action at all because my wife would fold up like an origami pet under the pressure, and to the perspective couple we all know what THIS looks like on the surface, right? Gross disinterest.
I do agree with the idea though that it shouldn't take several "dates" to figure out if you're gonna sack someone. It's swinging, not marriage.
Mr. P