Negativity alert 😔
The more I think about it, the less fond I am of having version-exclusive Gym Leaders. :/ (I know Black & White did it, but that was a while ago and I thought they'd moved on.) I'm not fond of version-exclusive anything besides Mons or other tradeable things (again, R/S did this prominently, but an alternative was later introduced in Emerald, and while OR/AS was good I wouldn't have minded Emerald being remade instead) - trading for version-exclusives is a pain, but it's doable, whereas exclusive Gym Leaders, etc. means you will not be able to have all the content without buying both games, period. I thought the official position was that the two-version system isn't meant to make you buy two games, but to encourage trading and socialization?
Yes, I know I could just pick solely based on the Gym Leader I like and trade for my preferred box legendary - but I don't just want to have Zacian, I want to see it as a figure in the story and have an epic battle at the climax to catch it. The entire concept of box legendaries is meant to get you hyped up for this! (Imagine if for some reason you bought Sun over Moon despite preferring Lunala, figuring you could trade for one, and then you found out what the deal really was with that particular box legendary...) And what if, for example, there ends up being two pairs of version-exclusive Gym Leaders, and you prefer the one from Sword out of the first pair and the one from Shield out of the second? Or the Gym Leaders and another untradeable version-exclusive feature to choose between? I just don't like this.