Used this as a base: [link]

I am against all Genderswap X Their counterpart. I will be making separate ones, so expect more.

On all pairings: Sorry, but its just really stupid. It's not the selfcest, its the fact they're exactly the same character. While they would get along well, they have a high chance of getting sick of eachother, because they would think exactly alike, act exactly alike, and would get sick of the constant similarity of their lifestyle. Beyond that, there isn't any chance for growth of character. They would settle in to the same exact patterns as before, learning nothing from their time together. Even pairings like Fluttermac, with their high similarity, they are at least different characters. They've had different lives and experiences, they can settle into a new lifestyle, and grow as characters. And from a foal standpoint, even if you discount deformities due to the incest aspect, they're just clones of their parents, And if you take into account their parents or siblings genetics, you've still only got a limited set of colours, because theyre, again, just the same characters, just as the opposite sex.

On Elusity: Elusity is definitely the one that makes the most sense out of all of them. Rarity and Elusive are both narcissistic ponies, and probably would be attracted to eachother, and there's no question about that. But think about the way they act, Elusive would be a gentlecolt, and Rarity would be demanding of such a thing, but in the end, the push and pull would end up making them angry at eachother, Elusive would eventually get sick of being nice and gentlecoltly, as even he would eventually wear down, and Rarity would be disappointed that he isn't her dream stallion. If that doesn't happen, their compulsions would interfere with eachother, as eachothers "organized chaos" would drive eachother mad, because both of them would see it as not their "organized chaos" but mess. And if they got over that, they would just settle down and be exactly the same, both need somepony to show them that even if their dreams don't match reality, sometimes reality is good enough. They've both had the same experiences, they've both been through all the same character developement, and that makes for no more character developement, unless they run into those problems, which would probably split them apart.

BE RESPECTFUL WITH COMMENTS, PLEASE. Making a case in favor of this is different than "OMG YOU SUCK FOR BEING AGAINST THIS".