With the Turd in Chief flailing to stay above water at the moment, and the rabid anti-gunners temporarily appeased, I give it a 50/50 chance that the prohibitions come into force before the writ drops for an election. Trudeau is already going to lose a few rural ridings over C-71, and things are too close right now for him to risk any more. Any more messing with guns is likely to wait until after the election now.
The 858/Swiss-Arms banpocalypse will require an Order In Council, which is a fairly "public" thing to do. And it isn't 100% clear which 858's are going to be on the chopping block. The RCMP have admitted they don't have a faint foggy clue how many of these rifles are in the country, how they would go about convincing people to register them, and what the administrative process will be to grandfather possibly as many as 15,000 (or more) license holders with spiffy new 12.x licenses.
Both the Liberals and the RCMP are terrified of another non-compliance fiasco, which was the true reason for the death of the original registry. Estimates are that as little as 50% of the guns in the country were registered - and that's terrible optics for the "civilized, polite, law abiding" citizenship that our government likes to portray Canadians as on the world stage.
But that's assuming a rational and sane Liberal Leadership, which is a dangerous assumption to make at the best of times.