So...do we have a brewing recipe for this Luck Potion yet? Neither the Wiki nor the snapshot changelog has it.
My guess: brew a fermented spider eye onto potion of leaping. Or make it only obtainable from killing witches or something.
On the one hand, if this is an easily obtained potion from farmable ingredients, it's kind of overpowered, and no one is gonna want to open a loot chest or slaughter a bunch of mobs in a grinder without quaffing a luck potion first. But make it too hard to obtain...and no one is gonna want to open a loot chest without quaffing one, so a multiplayer server is gonna be filled with "DO NOT OPEN THIS CHEST YET" signs and ticked-off players angry at newbs for opening the chests they found while caving.
My interpretation was that this potion only affects item drops or rather items that are generated on the spot after killing mobs, fishing, etc.
When a player finds a chest it and its loot has already been generated long ago, so a potion of luck should have no effect on those.