It was SOP for some operators at least 30 years ago - the only caveat was that a cooldown period (maybe 2 minutes) should be observed unless negligible R/T was used.
In fact, 40 years ago I rode a DL DC-6 into ORD and noticed R-2800 #4 was idling slower than the others during the long taxi. It finally died well before we reached the gate------ but I doubt this was intentional.
