Swain and LeBlanc's intertwined lore was discussed on the /r/SwainMains subreddit recently actually, and both Reav3 and Interlocutioner (narrative writer for Swain's VGU) commented on the thread.
Quoting from Interlocutioner's response:
Hey Spyro, I'm not working on Sion but I am the narrative writer on Swain. Per this general discussion, a lot of the Noxian cast may shift a tiny bit as we start to understand more about how Swain really rose to power, and we'll update things the best we can to reflect this!
We definitely have something in mind for his relationship with LeBlanc...
That's all I can probably say. A tiny bit more than u/Reav3 [+1] did. :D
I think they would definitely still keep the whole 'conspiring for mutual power' part as canon. Her posing as Jarvan IV in Kalamanda is more or less confirmed by the Sion Reborn teaser.
But I am actually more interested in their personal relationship to each other.
It was implied in LeBlanc's League Judgement that she at least, has or had some affection for Swain. Though, Swain was noticeably colder to her in the Sion Reborn dialogue (she even notes they don't see each other as much as before).