All that is is a Continuous Descent Approach. No big deal at all. Every modern jet can do them at near idle power. In the 717, a small amount of "fat" (too much, in my opinion) is built in so that if unexpected tailwinds are encountered, the aircraft can still stay on/get back to the ideal descent profile and to provide a safe approach. Spinning up from Flight Idle just before touchdown is not desirable.
The big problem is ATC and other traffic getting in the way, requiring either lower-than-desired profiles, non-optimum speed or hold-ups.
If one operator does successful CDAs, then another is being unfairly penalised because they are being kept out of the way.
I believe all this bluster about CDAs and RNP is just a smokescreen for an ATC system which cannot cope with the traffic levels.