Personally, I think the Banshee's and Abyssal stat swap is confusing and much more complicated than it needs to be, primarily because Banshee's Veil has always been a purely defensive item and Abyssal Scepter has always been a utility offensive item (at least, for the 4 seasons that I've been playing).
Is the balance team so obsessed with an item's "identity" that they would rather swap EVERY stat EXCEPT the unique passives instead of swapping JUST the unique passives...? That sounds really dumb, honestly.
I'd much rather buy the new Abyssal Scepter and say "oh, that's right, this has a new passive (spell shield)" rather than re-train myself to buy a completely different item. Plus, I would have to swap the two items in every AP item set, that's just annoying.