The one place I'd be happy to see D:OS2 material would be if that wizard/merchant from D:OS2, who left Rivelon to go planes-hopping in search of other forgotten realms... has a little shop in Baldur's Gate, and sells paraphernalia from his planes-walking adventures, including relics form Rivelon. That, to me, would be an acceptable level of insertion, because it can actually fit within the existing realms lore, while still being a hat tip to the developers and their past projects.
I'd quite like to see that sort of thing: brief cameos from other reality-hopping characters like Ciri from The Witcher and Elizabeth from Bioshock would be fun although probably very painful in terms of IP so I don't see it happening, at least outside of user-made mods (I have the latter and a bunch of Elves from Dragon Age in Fallout 4, for example, precisely because they don't belong there!) But I can also see that they would irritate other people quite a lot so maybe it's better to play it safe...
