What does the Supreme Court's new dog search case mean?

So the Court announced a new ruling yesterday (4/21) covering dog searches. (case here). In summary:

A police officer pulled over a motorist for driving on the shoulder of the road. The officer finished writing the ticket, checking for warrants and gave the driver the ticket. The police officer asked the driver if he could search the car with his dog, and the driver said no. The officer then said the driver was not free to leave, and called for back-up. After about eight minutes, a backup officer arrived and the first officer then deployed his dog. The dog alerted, and the officers found some methamphetamine.

The question was, could the officer hold someone on the grounds of a traffic stop in order to conduct a more extensive search for criminal activity?

The Court ruled no. The Court held that the officer must conduct the traffic stop efficiently, with an eye on completing the "mission" of the traffic stop. (Issuing the ticket, running the background check, etc.) They ruled that the officer cannot extend the stop after completing the mission nor can he delay the completion of the mission so that he can complete the secondary criminal investigation.

The dissent argues that this is an unclear line that creates a one-way ratchet that requires officers to move faster and faster, because the less efficient officers are unlawfully extending the stop. With respect to Justice Thomas, I think he misreads the decision.

It will not come down to a stopwatch analysis where the officer has to complete the stop within, say 14:21. Rather, the analysis will come down to the question of "Did the officer extend the stop in order to pursue something outside the mission of the stop?"

This, finally, is some kind of check on the use of drug dogs to eliminate the Fourth Amendment, in that the police can't make drug dog searches routine, because they extend the stop outside of the mission.

This does not limit the ability of police to engage in searches based on reasonable suspicion gained from the traffic talk. If the police stop a driver for speeding, and smell marijuana, they can keep the driver and search the car because there's evidence of criminal activity. What they can't do is keep every driver (or random drivers) to bring drug dogs to search "just in case".