This will be great on days where there are delays.
But on days where you get right to the runway, or right to your gate, you're already skirting the minimum time limits for running the engine. On a cold day, even in Newark, when it's not busy, you've got to crank both engines at the gate just to get the engines warmed up enough to be able to takeoff.
The same goes for coming into the gate. Small airport/quick taxi/you have a minimum amount of time the engines need to run before shutting them down. Again, I've had this take less than 2 minutes, and we're sitting in front of the gate running the engines.