Plarium, how about giving us a double artifact drop in every dungeon that last for 1 day. It will not only benefit the players but the company as well. Because :

1: it last a day

2: when pay to play players are out of energy they will buy more because this is an event that will be worth buying energy, and who knows maybe f2p player might be tempted to buy energy 

3: it's a good way to make players waste their gems on energy which in return helps you cause they'll probably purchase more.