Many a times you do not want to either pick a call or reject it, but let it ring till it drops off. Works great when the caller is your boss or someone’s feelings you do not want to hurt 
. In such situations, pressing the center button to just silence the call on the dashboard (and on the phone) to avoid distraction was a good implementation.
In case the devs need a base to kickstart, the below app that connects to your smartwatch implements this feature by receiving a touch from the smartwatch to activate DND on phone till the call hangs up on the companion app, effectively stopping the ringing. Best part, it is open source!