Guys i need to talk about this shipp, i swear that it makes sense, let me explain;
I was planning to write a story, in which this shipp was the main reason for the plot to develop, but as I'm very lazy it didn't even come out of my head, and I didn't even have a script, but as I see that this shipp in question has so much talk since 3 years ago, I'll tell you a little bit what went through my troubled head so that the two would get to know each other:
At the time Cadance gave birth to Flurry Heart, she and Shining were in a lot of conflict, as raising a baby is not easy, and Cadance did a lot of things to distract herself from this difficult life,So on one of her days off, she ended up meeting fleur de liss and they became friends, but at the same time she was also having problems in her marriage, as her husband was stubborn and busy. Blaming herself about for perhaps not being able to make her marriage last much longer, and soon they considered falling in love with each other and living together because both They felt comfortable in the presence of the other, On the other hand, things with Shining went from bad to worse, both ended up getting divorced from their respective husbands, d were a symbol of freedom for the entire population of equestrian ponies.
Basically that would be the basis of something I would create, of course it would have more plot involving the two relationships, but as it's a summary to explain the weird "SHIPP" between the two :)