Against Sunset Whatshername
I wrote a whole omake about this pony. But I don't think I want to see her in the quest.
Bird likes to say that we the voters represent Velvet's subconscious. That creates a dissonance when canon pieces come into play. When there are characters who we as voters are committed to and have long-standing relationships with and want to see, relationships Velvet does not have. Conversely, I think there are things that Velvet values — the Glory — that we voters don't care quite as much about. We like seeing characters we like and are invested in interact, we've voted for that constantly, climbing the Mansus we had to be nudged and then shoved towards.
Twilight is the most obvious example here. I can accept it though, given the way it was built up in story. Sure, Velvet values Twilight more than she values 500 bits, guilt and regret are that strong. I may wish it was otherwise, wish I wasn't pretty certain that if we were offered a Twilight option tomorrow we'd take it in a heartbeat… but I can see it. It fits.
Sunset Shimmer would not fit. I buy that a lot of people quite like her and find her interesting and a fun character and want to see her. What I don't buy is why Velvet would. In this strange world, why she would focus on a pony she does not know and has never met. I can buy there's a resonance, but it just feels like it would be so much so something imposed by us readers on Velvet, not something organic.
I know, trust the QM. And I do trust Bird's capacity to make it natural, and make it flow, and make it work. But I don't think it would eliminate the dissonance between how we readers would react to a Sunset hook (absorption?) and how Velvet would (perhaps mild interest?). And I would find that frustrating.