I have done the cuckold 69 position with couple's and I don't think that there is anything wrong it. I am a straight man and don't get fluffed or do any kind of man on man sexual contact. Dping those holes sometimes even the same one is as close as it gets.
I have done the whole cuckold 69 and blown loads inside the wife, got up, and hubby's eat it out of them. If that was his thing then it is what it is but as far as there being some kind of philosophy behind it as good for the whole sexual experience i have never thought about it and have done this position with couple's quite a few times.
Understand something a good bull understands that the whole threesome with a couple is more about their fantasy being fulfilled then a bull getting laid and fucking some married pussy. As long as what they want to do does not violate my clear sexual orientation boundaries well then I'm down for whatever!
See once I establish that I am straight my mind doesn't entertain thoughts that I am somehow being tested or pushed into doing something that I just don't do! That also why I always say that I would never say or do anything to a mans wife that I wouldn't do in front of him.