Idk if you know but there us is a chance that you get fortune boxes on levels which aren't boss levels
I have gotten plenty of fortune boxes from OD 6
However, there is a catch to it, you only get them on normal/easy difficulty, if you farm hard or insane, you wont get them
I agree with your idea of this new event and this has been discussed on the old forums as well and I'll be happy if this becomes a thing.
Now its up-to team Gato to implement this
Welcome to the forum btw