It is obvious the main reason OOO removed wasn't to "let players play more" but to make people pay full price for supply depot stuff and to end alt crafting, otherwise they would have kept it or simply reduced the elevator cost. The fire crystals part of that update was meant to balance free orbs dropping, not the free elevator cost. mist was something they surreptitiously removed among the numerous other things that changed in the update so that players would not complain too much about its removal.
I suggest bringing it back, except with a cap of 50 daily, with an elevator cost of 2 energy. This way players have a way of getting a small discount on items they purchase if they don't have enough time to play that day, as well as allowing one to craft one two star item a day for free if they lack time. It should also fully regenerate over the same period of time. This provides a plenty amount of runs for the players, and helps those who do not have as much time daily.
Since energy is only used for buying things from the supply depot (you can buy unbind tickets there), bribing krogmo and opening danger rooms, what you're suggesting is to give everyone 50 CE off their first purchase every day or 2 free plays at krogmo and to make danger rooms free. I guess it would also allow for a single revive and free to cheap turrets/friendly mechas or so as well.
I wouldn't mind being given any of these things, but I will say that free elevators more than compensate for the lack of them. I'd much rather Three Rings just make radiant fire crystals more plentiful, or to at least fix the treasure boxes after Operation Crimson Hammer, which drop mostly shinning fire crystals somehow.