I think I saw someone using this item build in a game I recently played. I don't know if it was you or someone just trying out this, but they dominated our Malzahar. (I have no idea how it's possible for Malzahar to lose to Orianna)
I didn't try this myself, but based on what I saw and how that Orianna carried the game I think this is a very viable build. But ofc with a char with hardest difficulty you need skill, not only an item build.

After I get over my first games trying Orianna (and failing miserably) I will try this and then vote.

mmm... AP carry with 379 AP end game? Do you know what carry mean?