I really like all the mane six except for S8+ Twilight
, they all are great, I'd be comfortable with any of them. Or all of them.
I wouldn't like to be in a love triangle, or a herd, or anything like that though, but I feel that Dash has a special bond with all her friends, and I feel it could work.
I know it's an extremely unpopular thing to say, but after all they've been through together, I feel they probably have a shared intimacy. Not a romantic thing or anything, but still a friendship, albeit stronger and deeper than a regular friendship.
I don't think they spend the day fucking like bitches in a porn movie, I don't even think it'd really be a big part of their bond, but I don't think it'd be a taboo for them either.