I wouldn't hold my breath if I were you in regard to Larian's sixth gift bag, there a big chance that it will be canceled, just like the Fallen Heroes (Yep, it's factually dead). But even if next gift bag will come out of the closet, it's probably will be just as vexing as the fifth was (Two best armor sets you get at the very end of the game, when you don't really need them).
Ideally, sixth gift bag should have been quest bag, in order to tied up the story of the D:OS2. For example with the return of Zandalor and, maybe, cameo of Imps and Orcs with their champions.
But, if gift bag will even appear, it will probably contain some weapon pack or something equally cosmetic to the gameplay.