Where you will make the company money is with a
constrained optimized descent
This involves using idle descent from FL400/350 down to FL50, and driving the ac through the approach. This allows ATC to manage the mult-variant que, provide separation, and timing, WITH current ATC tools.
The pilot can calc TOD knowing current weight and MET, and the variable TOD can be managed as the FL50 point is set with speed, as an example of 210.
This way, all of the ac in the que have the same basis point for ATC to manage, and the beauty of a constrained optimized descent.
The fuel savings are much more than idle descent final approach.