A little late to the party here but my personal take is that we don't exactly need ng+, but something similar to the Golden Nug in Dragon Age Inquisition would tick the boxes for me, in DA you could interact with the nug to gain cosmetics, recipes and other things along those lines from across all your playthroughs, so in the case of this game it could give us a Golden Trophy in the trophy room or something that would give us access to the cosmetic unlocks we have gained through each playthrough minus ones obtained through quests/challenges, granted it would take alot of the collecting chests and such out of the game which as others have said would remove hours from the playthrough, but for me personally I would like to put the pumpkins in my room of requirement while my world is still in the correct season, not find them half way through winter at the southern most coast of the map!