Meat will take on smoke flavor for as long as the meat isn't wrapped. Now what does happen at the 140 internal temp mark is that the smoke ring will no longer form.
If you want a more smoke flavor, smoke longer with no wrapping. The smokiest flavor you will get will be cooking low and slow on a stick burner with no wrapping. Also using greener stronger woods like mesquite and hickory.
IMHO there is diminishing returns when it comes to smoke flavor (unless you are running a dirty fire) After 4-5 hours in the smoke, you really won't taste much more. Another way to ensure you are tasting smoke is to take a hot shower, clear out your sinuses, brush your teeth, and change your clothes prior to eating. When you are sitting around your pit, your sense of smell gets over saturated with the smell of smoke, which in turn makes it so you can't taste it as much. This is why if you eat your bbq the next day, you can smell and taste the smoke much better than you do the day you cook it.