It is not only safe, it is ideal.
We as pilot would love to have this system in place already as it results in a reduced workload and allows us to direct our attention to other areas of the flight. One of the biggest areas of mistakes (or "pilot deviations" in our lingo) happens when aircraft are assigned complicated crossing restrictions on descent. It becomes easy to make a mistake and get too close to other aircraft. Implementing this system would go a long way towards eliminating those mistakes.
And just in case you are worried, we generally descend at idle power all the time. We always have to add power back when we are forced to level off. There would be no difference in the pilot technique used to land like this compared to what we use now, it would just use less fuel, make less noise, eliminate many potential traffic conflicts, and make your flight cheaper.