Rule of thumb - Acft slow down 10 KIAS every nm in level flight.
Read somewhere (maybe Av & Tech) ATC is testing new software sys in SFO. They send a CPDLC msg to cruising acft with a suggested lateral & vertical path in order to maintain a CDA at idle thrust setting, considering all the expected inbound traffics. If accepted it becomes a clearence. Seems it's working good.
HVIII