I think DD won't change at least not now.The chest is not a bad idea but the time between DD is absurd 6 hours it's too long.You can do only 1 or 2 DD in a day and if you have the item you need you are very lucky.
I agree with you the time between DD is absurd and you're lucky if you drop items you need.I did Karrundax 40 times for my swashbuckling gauntlet and now i have to do Spellplague and i don't want to do it 40 times so a chest in every dungeons is a goog idea